Add changelog entries for 12.1.6

[emelsimsek]

Add changelog entries for 12.1.6.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.64%. Comparing base (15ecc37) to head (d9d122e). Report is 3 commits behind head on release-12.1.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release-12.1 #7742 +/- ## ============================================= Coverage 89.64% 89.64% ============================================= Files 274 276 +2 Lines 59575 59653 +78 Branches 7435 7446 +11 ============================================= + Hits 53407 53477 +70 - Misses 4036 4041 +5 - Partials 2132 2135 +3 ```

[emelsimsek]

@microsoft-github-policy-service rerun