ci: use caching to speed up workflows (#760)

Use caching to speed up workflows: 9-14 minutes (ish) to 6-8 minutes (ish)

Commits:
* ci(release): use GitHub cache

* ci(release): restore signing

.github/workflows/pull-request-build.yml

@@ -20,10 +20,12 @@ jobs:
         with:
           java-version: '17'
           distribution: 'zulu'
+          cache: 'gradle'
       - name: Setup Flutter
         uses: subosito/flutter-action@v2
         with:
           channel: 'stable'
+          cache: true
       - name: Install Flutter dependencies
         run: flutter pub get
       - name: Generate files with Builder

.github/workflows/release.yml

@@ -23,6 +23,7 @@ jobs:
         with:
           java-version: '17'
           distribution: 'zulu'
+          cache: 'gradle'
       - name: Setup Node.js
         uses: actions/setup-node@v3
         with:
@@ -32,6 +33,7 @@ jobs:
         uses: subosito/flutter-action@v2
         with:
           channel: 'stable'
+          cache: true
       - name: Install Flutter dependencies
         run: flutter pub get
       - name: Generate files with Builder
@@ -64,4 +66,4 @@ jobs:
       - name: Release
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: npm exec semantic-release
+        run: npm exec semantic-release