ci: update GitHub Actions worflows

ci: use clang-format-12

(cherry picked from commit 7e1a2d8)

ci: replace windows-2016 agent

(cherry picked from commit 9e60f81)

ci: use actions/checkout@v3

(cherry picked from commit d848720)

ci: fix iwyu

(cherry picked from commit 47868f9)

feat(push): Add method to delete metrics for instance

Fixes: jupp0r#303

fix(core): Locale-independent floating-point serialization

Fixes: jupp0r#509

Prepare v0.12.3 release

core: avoid collecting empty metric families

Merge pull request jupp0r#453 from jupp0r/fix-std-tochars

core: Fix usage of std::to_chars

Merge pull request jupp0r#435 from jupp0r/improve-example

pull: Add better example

pull: Use internal base64 decoding function to avoid dependency (jupp…

…0r#417)

chore: Raise version to v0.10.0 due to changed public interface

chore: Raise version to v0.10.0 due to changed public interface