fix(ci): pass the release keystore to Gradle as an absolute path (#1426)

The release build has failed since the AGP 9.4.0 bump:

    Execution failed for task ':apps:flipcash:app:validateSigningRelease'.
    > Keystore file '/home/runner/.gradle/daemon/9.7.1/key/key' not found
      for signing config 'externalOverride'.

`base64-to-file` reports a workspace-relative `key/key`, which the workflow
passed straight through as `android.injected.signing.store.file`. AGP resolves
that property against the Gradle daemon's working directory rather than the
project, so it looked for the keystore under `~/.gradle/daemon/9.7.1/`.

Prefix the path with `github.workspace`. That also retires the second decode
into `apps/flipcash/app/key/` — it only existed to cover the module-relative
resolution, and nothing in the build reads that location.

Author: bmc08gt

.github/workflows/build-fcash2-upload-android.yml

@@ -127,21 +127,14 @@ jobs:
           fileDir: ./apps/flipcash/app/src
           encodedString: ${{ secrets.FLIPCASH2_GOOGLE_SERVICES }}
 
-      - name: Decode Upload Key Store file into location 1
+      - name: Decode Upload Key Store file
         uses: timheuer/base64-to-file@v1
         id: signing_key
         with:
           fileName: key
           fileDir: ./key
           encodedString: ${{ secrets.UPLOAD_KEY_STORE }}
 
-      - name: Decode Upload Key Store file into location 2
-        uses: timheuer/base64-to-file@v1
-        with:
-          fileName: key
-          fileDir: ./apps/flipcash/app/key
-          encodedString: ${{ secrets.UPLOAD_KEY_STORE }}
-
       - name: Setup BugSnag API Key
         run: echo BUGSNAG_API_KEY=\"${{ secrets.FLIPCASH_BUGSNAG_API_KEY }}\" > ./local.properties
 
@@ -157,7 +150,10 @@ jobs:
       - name: Build release
         run: bundle exec fastlane android build_flipcash
         env:
-          STORE_FILE: ${{ steps.signing_key.outputs.filePath }}
+          # base64-to-file reports a workspace-relative path, and AGP resolves
+          # android.injected.signing.store.file against the Gradle daemon's working
+          # directory, not the project — so pass it absolute.
+          STORE_FILE: ${{ github.workspace }}/${{ steps.signing_key.outputs.filePath }}
           STORE_PASSWORD: ${{ secrets.KEYSTORE_PASSWORD }}
           KEY_ALIAS: ${{ secrets.KEY_ALIAS }}
           KEY_PASSWORD: ${{ secrets.KEYSTORE_PASSWORD }}