ci: remove outdated Ubuntu 20.04 and macOS 12 from compatibility matrix

These platforms are no longer actively supported and causing CI delays.
Keeping focus on current LTS platforms: Ubuntu 22.04 and macOS 13.

Author: avrabe

.github/workflows/production-readiness.yml

@@ -117,7 +117,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-20.04, ubuntu-22.04, macos-12, macos-13]
+        os: [ubuntu-22.04, macos-13]
 
     steps:
       - uses: actions/checkout@v5