Add Dependabot and improve build pipeline (#23)

* Add dependabot config

* Update actions/cache and simplify variable usage in build

.github/workflows/tests.yml

@@ -16,6 +16,9 @@ jobs:
     strategy:
       matrix:
         php-version: ['7.4', '8.0', '8.1']
+        include:
+          - php-version: '8.1'
+            run-sonarqube-analysis: true
 
     steps:
       - uses: actions/checkout@v2
@@ -41,7 +44,7 @@ jobs:
           echo "::set-output name=dir::$(composer config cache-files-dir)"
 
       - name: Cache Composer dependencies
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
@@ -55,7 +58,7 @@ jobs:
 
       - name: Run SonarQube analysis
         uses: sonarsource/sonarcloud-github-action@master
-        if: matrix.php-version == '8.1'
+        if: matrix.run-sonarqube-analysis
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           SONAR_TOKEN: ${{ secrets.SONARCLOUD_TOKEN }}