docs: add 0.12.2 release to CHANGELOG #1436

Job	Run time
Valgrind	52s
Windows CMake, Release configuration	1m 54s
Clippy	18s
Build+test (clang, stable, ubuntu-latest)	51s
Clippy nightly (optional)	16s
Build+test (clang, beta, ubuntu-latest)	55s
Check for documentation errors	19s
Build+test (clang, nightly, ubuntu-latest)	58s
ensure-header-updated	1m 0s
Build+test (clang, 1.61.0, ubuntu-latest)	1m 49s
Format	16s
Check minimum versions	38s
Build+test (gcc, stable, ubuntu-latest)	50s
Windows CMake, Debug configuration	1m 22s
Build+test (gcc, beta, ubuntu-latest)	48s
Build+test (gcc, nightly, ubuntu-latest)	49s
cargo-c	31s
Build+test (gcc, 1.61.0, ubuntu-latest)	1m 49s
Clang Tidy	8s
Build+test (macos-latest, clang, stable)	2m 26s
Miri	54s
	19m 43s

Provide feedback