chore: fix concurrency execute with melos.

[wasabeef]

What does this change?

I limited concurrent execution because these logs were being output during the execution of the flutter command.

When melos run get

ERROR: ERROR: [example]: Waiting for another flutter command to release the startup lock...
ERROR: ERROR: [flutter_gen]: Waiting for another flutter command to release the startup lock...
ERROR: ERROR: [flutter_gen_runner]: Waiting for another flutter command to release the startup lock...

And fix analyze.

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Checklist:

Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• [ ] Make sure to open a GitHub issue as a bug/feature request before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
  • [x] Ensure the tests (melos run test)
  • [x] Ensure the analyzer and formatter pass (melos run format to automatically apply formatting)
• [ ] Appropriate docs were updated (if necessary)