Fix container app create not waiting for ready environment

[p-bouchon]

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• Have you run azdev style <YOUR_EXT> locally? (pip install azdev required)
• Have you run python scripts/ci/test_index.py -q locally?

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[azure-client-tools-bot-prd]

Hi @p-bouchon,
If you want to release the new extension version.
Please write the description of changes into HISTORY.rst and update setup.py.

[yonzhan]

Thank you for your contribution! We will review the pull request and get back to you soon.

[zhoxing-ms]

@p-bouchon Please take a look at this comment #6399 (comment) first.