Go back to defaulting to exact

We should probably default to the safest behavior, given that the purpose of a tool like Pants is correctness.

This also avoids making a breaking API change.

# Rust tests and lints will be skipped. Delete if not intended.
[ci skip-rust]

# Building wheels and fs_util will be skipped. Delete if not intended.
[ci skip-build-wheels]

src/python/pants/backend/python/goals/setup_py.py

@@ -328,7 +328,7 @@ def register_options(cls, register):
         register(
             "--first-party-dependency-version-scheme",
             type=FirstPartyDependencyVersionScheme,
-            default=FirstPartyDependencyVersionScheme.COMPATIBLE,
+            default=FirstPartyDependencyVersionScheme.EXACT,
             help=(
                 "What version to set in `install_requires` when a `python_distribution` depends on "
                 "other `python_distribution`s. If `exact`, will use `==`. If `compatible`, will "

src/python/pants/backend/python/goals/setup_py_test.py

@@ -216,7 +216,7 @@ def test_generate_chroot(chroot_rule_runner: RuleRunner) -> None:
             "packages": ("foo", "foo.qux"),
             "namespace_packages": ("foo",),
             "package_data": {"foo": ("resources/js/code.js",)},
-            "install_requires": ("baz~=1.1.1",),
+            "install_requires": ("baz==1.1.1",),
             "entry_points": {"console_scripts": ["foo_main=foo.qux.bin"]},
         },
         "src/python/foo:foo-dist",