ci: add develocity key explicitly

The `DEVELOCITY_ACCESS_KEY` environment variable should be set by the `setup-gradle` action. However, it does not seem to work in this repo. Trying to set it explicitly on each step.

.github/workflows/gradle.yml

@@ -36,10 +36,14 @@ jobs:
       - name: "🏃 Run Tests"
         if: github.event_name == 'pull_request'
         id: tests
+        env:
+          DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
         run: ./gradlew check
       - name: "🔨 Build project"
         if: github.event_name == 'push'
         id: build
+        env:
+          DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
         run: ./gradlew build
       - name: "📄 Publish Test Report"
         if: steps.build.outcome == 'failure' || steps.tests.outcome == 'failure'
@@ -56,6 +60,8 @@ jobs:
       - name: "✍️ Generate Documentation"
         id: docs
         if: success() && github.event_name == 'push' && matrix.java == '17'
+        env:
+          DEVELOCITY_ACCESS_KEY: ${{ secrets.DEVELOCITY_ACCESS_KEY }}
         run: ./gradlew docs
       - name: "📤 Publish to Github Pages"
         if: steps.publish.outcome == 'success' && github.event_name == 'push' && matrix.java == '17'