fix: Run melos bootstrap before publishing

[mugikhan]

Description

Version solving fails if the pubspec_overrides.yaml is not generated before running melos publish (dart pub publish --dry-run). It tends to look for a new version online before it has been published. This change ensures that the override is present before trying to validate the pubspec.

Work done

• Add step to install dependencies and generate a pubspec_overrides.yaml so that version solving does not fail when validating the pubspec with melos publish.
• Only run publish workflow once per tag push