Update azure-container-webapp.yml

Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

List which issues are fixed by this PR. You must list at least one issue.

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

Pre-launch Checklist

[ ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
[ ] I read the Tree Hygiene wiki page, which explains my responsibilities.
[ ] I read the Flutter Style Guide recently, and have followed its advice.
[ ] I signed the CLA.
[ ] I listed at least one issue that this PR fixes in the description above.
[ ] I updated/added relevant documentation (doc comments with ///).
[ ] I added new tests to check the change I am making, or this PR is test-exempt.
[ ] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.