always run pitest in github job

.github/workflows/gradle.yml

@@ -31,4 +31,4 @@ jobs:
         java-version: '17'
         distribution: 'adopt'
     - name: Build with Gradle
-      run: ./gradlew build
+      run: ./gradlew build pitest

.github/workflows/mutationtests.yml

@@ -1,34 +0,0 @@
-name: Run mutation tests
-
-on:
-  push:
-    branches: [ main ]
-  pull_request:
-    branches: [ main ]
-
-jobs:
-  mutationtests:
-
-    runs-on: ubuntu-latest
-
-    steps:
-    - name: Checkout
-      uses: actions/checkout@v2
-    - name: Configure cache
-      uses: actions/cache@v2
-      env:
-        cache-name: mutationtests
-      with:
-        path: ~/.gradle/caches/build-cache*
-        key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ github.sha }}
-        restore-keys: |
-          ${{ runner.os }}-build-${{ env.cache-name }}-
-          ${{ runner.os }}-build-
-          ${{ runner.os }}-
-    - name: Set up JDK 17
-      uses: actions/setup-java@v2
-      with:
-        java-version: '17'
-        distribution: 'adopt'
-    - name: Run mutation tests
-      run: ./gradlew pitest