fix: Decode signing key directly into file

This commit simplifies the decoding of the signing key by directly writing the decoded output to the keystore file, rather than using a temporary file.
It also adds the absolute path of the release store file to the environment for use in subsequent steps.

.github/workflows/android_ci.yml

@@ -39,8 +39,8 @@ jobs:
             ENCODED_STRING: ${{ secrets.SIGNING_KEY_STORE_BASE64 }}
             SIGNING_KEY_STORE_PATH: ${{ secrets.SIGNING_KEY_STORE_PATH }}
         run: |
-          echo $ENCODED_STRING > keystore-b64.txt
-          base64 -d keystore-b64.txt > "$SIGNING_KEY_STORE_PATH"
+          base64 -d <<< $ENCODED_STRING > "$SIGNING_KEY_STORE_PATH"
+          echo "RELEASE_STORE_FILE=$(realpath $SIGNING_KEY_STORE_PATH)" >> $GITHUB_ENV
 
       - name: Build with Gradle
         env: