Update blog post for FerretDB v1.6.0

[Fashander]

Description

Readiness checklist

• I added/updated unit tests (and they pass).
• I added/updated integration/compatibility tests (and they pass).
• I added/updated comments and checked rendering.
• I made spot refactorings.
• I updated user documentation.
• I ran task all, and it passed.
• I ensured that PR title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[mergify]

Marketing blog posts should be reviewed by @ptrfarkas and @AlekSi.

[codecov]

Codecov Report

Merging #3073 (bbe0d7d) into main (f4d396e) will decrease coverage by 0.07%.
The diff coverage is n/a.

❗ Current head bbe0d7d differs from pull request most recent head cc72db0. Consider uploading reports for the commit cc72db0 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3073      +/-   ##
==========================================
- Coverage   76.49%   76.42%   -0.07%     
==========================================
  Files         386      386              
  Lines       21165    21165              
==========================================
- Hits        16190    16176      -14     
- Misses       4050     4060      +10     
- Partials      925      929       +4     

see 4 files with indirect coverage changes

Flag	Coverage Δ
hana	?
integration	72.95% <ø> (-0.05%)	⬇️
mongodb	5.54% <ø> (ø)
pg	66.29% <ø> (ø)
shard-1	54.80% <ø> (ø)
shard-2	55.14% <ø> (ø)
shard-3	57.68% <ø> (-0.05%)	⬇️
sqlite	46.71% <ø> (-0.05%)	⬇️
unit	24.20% <ø> (-0.04%)	⬇️

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