.github/PULL_REQUEST_TEMPLATE.md inconsistency

[chewong]

• If the issue is to do with Azure CLI 2.0 in-particular, create an issue here at Azure/azure-cli

Extension name (the extension in question)

Description of issue (in as much detail as possible)

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scripts/ci/test_integration.py no longer exists but it is still referenced in https://github.com/Azure/azure-cli-extensions/blob/master/.github/PULL_REQUEST_TEMPLATE.md

[derekbekoe]

@chewong If possible, create a PR for this small change.