Only sign master branch builds

Author: jcansdale

.github/workflows/main.yml

@@ -54,6 +54,7 @@ jobs:
         GitHubVS_ClientSecret: ${{ secrets.GitHubVS_ClientSecret }}
 
     - name: Sign the VSIX
+      if: github.ref == 'refs/heads/master'
       run: tools/vsixsigntool/vsixsigntool.exe sign /f certificate.pfx /p '${{ secrets.CERTIFICATE_PASSWORD }}' /sha1 9c5a6d389e1454f2ed9ee9419cdf743689709f9c /fd sha256 /tr http://timestamp.digicert.com /td sha256 ${{ env.vsixContainer }}
 
     - name: Upload VSIX artifact