[macos-runner] Merge keychain unlock and fastlane into a single step

Identity was visible with find-identity inside the unlock step itself
but still invisible to fastlane in the next step - each run: block
likely spawns a distinct process/session on this host executor, so the
unlock doesn't survive across steps even though keychain search-list
membership does. Run unlock and fastlane in the same shell invocation
to remove that boundary entirely.

.gitea/workflows/beta.yml

@@ -47,15 +47,12 @@ jobs:
           }
           EOF
 
-      - name: Unlock keychain
+      - name: Unlock keychain and run fastlane beta
         run: |
           security unlock-keychain -p "${{ secrets.CI_KEYCHAIN_PASSWORD }}" ~/Library/Keychains/ci-signing.keychain-db
           security list-keychains -d user -s ~/Library/Keychains/ci-signing.keychain-db ~/Library/Keychains/login.keychain-db
           security default-keychain -d user -s ~/Library/Keychains/ci-signing.keychain-db
           security find-identity -v -p codesigning
-
-      - name: fastlane beta
-        run: |
           cd Darwin
           fastlane beta