Update github workflow to include client_secrets.json in Preview build

      - name: Write client_secrets.json
        uses: DamianReeves/write-file-action@v1.2
        with:
          path: app/src/main/assets/client_secrets.json
          contents: ${{ secrets.CLIENT_SECRETS_TEXT }}
          write-mode: overwriteclient_secrets.json

.github/workflows/build_preview.yml

@@ -86,6 +86,13 @@ jobs:
           contents: ${{ secrets.GOOGLE_SERVICES_TEXT }}
           write-mode: overwrite
 
+      - name: Write client_secrets.json
+        uses: DamianReeves/write-file-action@v1.2
+        with:
+          path: app/src/main/assets/client_secrets.json
+          contents: ${{ secrets.CLIENT_SECRETS_TEXT }}
+          write-mode: overwrite
+
       - name: Build app
         if: ${{ ! startsWith(github.ref, 'refs/tags/') && github.repository == 'komikku-app/komikku' }}
         run: ./gradlew assembleStandardRelease testStandardReleaseUnitTest --stacktrace