tests/azure/templates/build_container.yml: Quote requests with version

The version requirement for requests need to be quoted not to lead into
a pip install command issue.

This is related to PR #1089 (Pin requests to < 2.29 temporarily)

tests/azure/templates/build_container.yml

@@ -22,7 +22,7 @@ jobs:
     retryCountOnTaskFailure: 5
     displayName: Install tools
 
-  - script: pip install molecule-plugins[docker] requests<2.29
+  - script: pip install molecule-plugins[docker] "requests<2.29"
     retryCountOnTaskFailure: 5
     displayName: Install molecule