[Agent CI] Update signing pipeline to respect the new MinGit layout (#…

…3867)

* Add pattern to sign `*.pyd` files for 3rd party assemblies signing

.azure-pipelines/signing.yml

@@ -149,6 +149,7 @@ steps:
         bin\**\*.exe
         externals\**\*.exe
         externals\**\*.dll
+        externals\**\*.pyd
       UseMinimatch: true
       signConfigType: inlineSignParams
       inlineOperation: |