docs: fix changelog header to consistent size (#385)

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

CHANGELOG.md

@@ -23,7 +23,7 @@
 * fix type in docstring for map fields ([9e33102](https://github.com/googleapis/python-datacatalog/commit/9e331027aa40dcbe4e7880d18043d89aa6af6b2a))
 * update taxonomy display_name comment ([#338](https://github.com/googleapis/python-datacatalog/issues/338)) ([9e33102](https://github.com/googleapis/python-datacatalog/commit/9e331027aa40dcbe4e7880d18043d89aa6af6b2a))
 
-### [3.7.1](https://github.com/googleapis/python-datacatalog/compare/v3.7.0...v3.7.1) (2022-03-05)
+## [3.7.1](https://github.com/googleapis/python-datacatalog/compare/v3.7.0...v3.7.1) (2022-03-05)
 
 
 ### Bug Fixes
@@ -51,7 +51,7 @@
 
 * add autogenerated code snippets ([650ad39](https://github.com/googleapis/python-datacatalog/commit/650ad39b6620c764ea64f5c0f2498a0ea387a834))
 
-### [3.6.2](https://www.github.com/googleapis/python-datacatalog/compare/v3.6.1...v3.6.2) (2022-01-10)
+## [3.6.2](https://www.github.com/googleapis/python-datacatalog/compare/v3.6.1...v3.6.2) (2022-01-10)
 
 
 ### Documentation
@@ -60,7 +60,7 @@
 * fixing upgrading guide v2 ([#277](https://www.github.com/googleapis/python-datacatalog/issues/277)) ([76f152a](https://www.github.com/googleapis/python-datacatalog/commit/76f152ac59e81d1ac02adcba2cbc8b1bec3ff888))
 * **samples:** Add sample for PolicyTagManagerClient.create_taxonomy ([#37](https://www.github.com/googleapis/python-datacatalog/issues/37)) ([15feb5d](https://www.github.com/googleapis/python-datacatalog/commit/15feb5dba028faa153c72374eca20a72fa72705e))
 
-### [3.6.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.6.0...v3.6.1) (2021-11-12)
+## [3.6.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.6.0...v3.6.1) (2021-11-12)
 
 
 ### Documentation
@@ -95,14 +95,14 @@
 
 * add context manager support in client ([#240](https://www.github.com/googleapis/python-datacatalog/issues/240)) ([c403d1d](https://www.github.com/googleapis/python-datacatalog/commit/c403d1d5a637b23343b23e74debed5f8b4c5c12a))
 
-### [3.4.3](https://www.github.com/googleapis/python-datacatalog/compare/v3.4.2...v3.4.3) (2021-10-05)
+## [3.4.3](https://www.github.com/googleapis/python-datacatalog/compare/v3.4.2...v3.4.3) (2021-10-05)
 
 
 ### Bug Fixes
 
 * improper types in pagers generation ([322cf9e](https://www.github.com/googleapis/python-datacatalog/commit/322cf9e543147b0b40e3b044e5822acf12e2d216))
 
-### [3.4.2](https://www.github.com/googleapis/python-datacatalog/compare/v3.4.1...v3.4.2) (2021-09-24)
+## [3.4.2](https://www.github.com/googleapis/python-datacatalog/compare/v3.4.1...v3.4.2) (2021-09-24)
 
 
 ### Bug Fixes
@@ -114,7 +114,7 @@
 
 * **samples:** add entry group greation to custom entry sample ([#215](https://www.github.com/googleapis/python-datacatalog/issues/215)) ([24d78cf](https://www.github.com/googleapis/python-datacatalog/commit/24d78cf44dd0a4e29aa66daec137e8a618b60f29))
 
-### [3.4.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.4.0...v3.4.1) (2021-09-01)
+## [3.4.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.4.0...v3.4.1) (2021-09-01)
 
 
 ### Bug Fixes
@@ -143,7 +143,7 @@
 
 * Documentation improvements ([6abe29d](https://www.github.com/googleapis/python-datacatalog/commit/6abe29d21c7481aa836a103d99722adcfbf6a6d3))
 
-### [3.3.2](https://www.github.com/googleapis/python-datacatalog/compare/v3.3.1...v3.3.2) (2021-07-27)
+## [3.3.2](https://www.github.com/googleapis/python-datacatalog/compare/v3.3.1...v3.3.2) (2021-07-27)
 
 
 ### Bug Fixes
@@ -160,7 +160,7 @@
 
 * release as 3.3.2 ([#193](https://www.github.com/googleapis/python-datacatalog/issues/193)) ([7f38774](https://www.github.com/googleapis/python-datacatalog/commit/7f38774e4831122f5b645b911eed0f673e0f182f))
 
-### [3.3.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.3.0...v3.3.1) (2021-07-20)
+## [3.3.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.3.0...v3.3.1) (2021-07-20)
 
 
 ### Bug Fixes
@@ -184,7 +184,7 @@
 
 * omit mention of Python 2.7 in 'CONTRIBUTING.rst' ([#1127](https://www.github.com/googleapis/python-datacatalog/issues/1127)) ([#173](https://www.github.com/googleapis/python-datacatalog/issues/173)) ([a3d17d4](https://www.github.com/googleapis/python-datacatalog/commit/a3d17d4b485e757480040783259da234abec69a0)), closes [#1126](https://www.github.com/googleapis/python-datacatalog/issues/1126)
 
-### [3.2.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.2.0...v3.2.1) (2021-06-09)
+## [3.2.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.2.0...v3.2.1) (2021-06-09)
 
 
 ### Bug Fixes
@@ -203,7 +203,7 @@
 
 * add async client to %name_%version/init.py ([85e46e1](https://www.github.com/googleapis/python-datacatalog/commit/85e46e144d32a0d66bc2d7c056453951eb77d592))
 
-### [3.1.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.1.0...v3.1.1) (2021-03-29)
+## [3.1.1](https://www.github.com/googleapis/python-datacatalog/compare/v3.1.0...v3.1.1) (2021-03-29)
 
 
 ### Bug Fixes