Fix: Correct macOS release build and update versioning

The macOS release build was failing due to missing `checkout` and `setup-flutter` steps. These have now been added.

Additionally, the versioning logic in `pubspec.yaml` has been corrected to use the `BUILD_NUMBER` for the build version instead of a fixed `+1`.

Author: gabrielbmoro

.github/workflows/release_flutter_app.yaml

@@ -20,13 +20,16 @@ jobs:
           VERSION=${TAG#v}
           echo "Setting version to $VERSION"
           # Update pubspec.yaml
-          sed -i '' "s/^version:.*/version: $VERSION+1/" pubspec.yaml
+          sed -i "s/^version:.*/version: $VERSION+$BUILD_NUMBER/" pubspec.yaml
 
   build-android:
     runs-on: ubuntu-latest
     needs: setup-tag
 
     steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
       - name: Set up Flutter
         uses: ./.github/actions/setup-flutter
 
@@ -47,6 +50,12 @@ jobs:
     needs: build-android
 
     steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Flutter
+        uses: ./.github/actions/setup-flutter
+
       - name: Build macOS release
         run: flutter build macos --release