remove musl from ci as doesn't work on 1.21

Author: alecmocatta

azure-pipelines.yml

@@ -29,4 +29,4 @@ jobs:
         rust_target_run: 'x86_64-apple-darwin'
       linux:
         imageName: 'ubuntu-latest'
-        rust_target_run: 'x86_64-unknown-linux-gnu x86_64-unknown-linux-musl'
+        rust_target_run: 'x86_64-unknown-linux-gnu'