Remove ubuntu-20.04 from build-build matrix due to GH removal on 2025-04-15 (#309)

- More info at actions/runner-images#11101

Author: paulorsousa

.github/workflows/ci.yml

@@ -63,7 +63,7 @@ jobs:
   build-ubuntu:
     strategy:
       matrix:
-        platform: [ubuntu-22.04, ubuntu-20.04]
+        platform: [ubuntu-22.04]
     runs-on: ${{ matrix.platform }}
     steps:
     - uses: actions/checkout@v4