pin ubuntu version and exclude boost-test cov

Recently there have been issues with ubuntu-latest and the cov-app. Setting the ubuntu-version to 22.04, fixes this issues. 

Excluding the coverage of the test-files (boost-test) is important, otherwise we get misleading coverage numbers.

.github/workflows/coverage.yml

@@ -5,7 +5,7 @@ name: Test Coverage
 jobs:
   run-coverage:
     name: Build
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
 
     - uses: actions/checkout@v4
@@ -44,7 +44,7 @@ jobs:
       run: |
         cd build
         lcov --capture --directory . --output-file coverage.info
-        lcov --remove coverage.info '/usr/*' 'boost/*' 'c++11/*' --output-file coverage.info
+        lcov --remove coverage.info '/usr/*' 'boost/*' 'c++11/*' '/home/runner/work/ADOL-C/ADOL-C/ADOL-C/boost-test/*' --output-file coverage.info
         lcov --list coverage.info
 
       # Upload coverage report to Codecov
@@ -55,4 +55,4 @@ jobs:
         token: ${{ secrets.CODECOV_TOKEN }}
         flags: unittests
         name: code-coverage-report
-
+