Fixes #140665 by replacing use of setUpAll and teardownAll with setUp and teardown respectively.

My theory has to how this issue happened (and how this PR fixes it) is that setUpAll is not guaranteed to run after any setUp in any parent test groups. However, setUp is guaranteed to run after any set-up callbacks in parent groups. From the documentation:

If this is called within a test group, it applies only to tests in that group. The body will be run after any set-up callbacks in parent groups or at the top level.

Meanwhile, setUpAll has a weaker documented guarantee that applies only to other setUpAll calls:

If this is called within a test group, The body will run before all tests in that group. It will be run after any setUpAll callbacks in parent groups or at the top level. It won't be run if none of the tests in the group are run.

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 and followed the Flutter Style Guide, including Features we expect every widget to implement.
• 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.

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