docs: clarify --min-coverage and configuration

[unicoderbot]

Summary

Updates the help text for the --min-coverage flag to document that it implicitly enables coverage collection, matching the existing documentation for --show-uncovered.

Changes

• Updated --min-coverage help text in lib/src/commands/test/test.dart
• Updated --min-coverage help text in lib/src/commands/dart/commands/dart_test_command.dart
• Updated documentation in site/docs/commands/test.md
• Updated corresponding test expectations

The help text now reads: "Whether to enforce a minimum coverage percentage. Implicitly enables coverage collection when used alone." to match the behavior of --show-uncovered.

Closes

#1684

[marcossevilla]

@vgvbot investigate and fix CI failures

[unicoderbot]

On it, I'll address the review comments and push the changes.

• Preparing environment
  • Cloning repository
  • Setting up dev environment
• Reviewing feedback
• Working on changes
• Pushing updates

I've pushed changes to address the feedback.