use only one runner-image for github actions

reasons:
- the project is not dependent on the OS, such that it would warrant testing/building against different OS versions
- we did not see the benefit of having multiple OS versions so far
- reduce build matrix cardinality. we have 20 jobs right now. it takes a while until all are finished. reducing this to 10 would be a substantial improvement.

Author: goekay

.github/workflows/main.yml

@@ -6,7 +6,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-22.04, ubuntu-24.04 ]
+        os: [ ubuntu-latest ]
         java: [ '17', '21' ]
         db: [ 'mysql:8.0', 'mariadb:10.3', 'mariadb:10.4.30', 'mariadb:10.5.21', 'mariadb:10.6.14' ]
     runs-on: ${{ matrix.os }}