[ci] Add more dev dependency checks, and fix errors

[stuartmorgan-g]

• Adds build_runner, mockito, and pigeon to the list of dependencies that we expect to only be in dev_dependencies.
• Fixes the error message for violations; I had missed in initial review that the errorr message was the same as the one for non-repo-local depndencies, making it misleading about what the problem was and how to fix it. (Also fixed the indentation, which had always been wrong.)
• Fixes camera_avfoundation, which had a violation introduced in my recent PR to start the Pigeon conversion.

See flutter/flutter#117905

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 relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• 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.

[stuartmorgan-g]

I switched the structure to a loop-constructed test set where each test only checks one package, because it's easier to ensure that everything is actually being covered (e.g., that we don't add a package to the list of dependencies, but forget to add it to the error message, so that it looks like it's being tested but actually isn't).