[macos-runner] Fix build number bump - agvtool was silently no-oping

Upload rejected with "bundle version must be higher than previously
uploaded version: 1" - agvtool new-version requires VERSIONING_SYSTEM =
apple-generic, which this project never sets, so it did nothing every
run despite reporting success. Pass CURRENT_PROJECT_VERSION directly
via xcargs instead, parameterized from the job's run number.

.gitea/workflows/beta.yml

@@ -20,6 +20,7 @@ jobs:
       APPLE_ID: ${{ secrets.APPLE_ID }}
       ITC_TEAM_ID: ${{ secrets.ITC_TEAM_ID }}
       DEVELOPMENT_TEAM: ${{ secrets.DEVELOPMENT_TEAM }}
+      BUILD_NUMBER: ${{ gitea.run_number }}
 
     steps:
       - name: Checkout
@@ -32,11 +33,6 @@ jobs:
           git -c credential.helper= -c http.lowSpeedLimit=1000 -c http.lowSpeedTime=30 clone "$AUTH_URL" .
           git checkout "${{ gitea.sha }}"
 
-      - name: Set build number
-        run: |
-          cd Darwin
-          agvtool new-version -all ${{ gitea.run_number }}
-
       - name: Write App Store Connect API key
         run: |
           cat > Darwin/fastlane/apikey.json <<EOF