fix(manager/pub): prioritise SDK version constraint from pubspec.yaml over pubspec.lock

[zeshuaro]

Changes

For the pub manager artifacts update, prioritise to use the SDK version from pubspec.yaml over pubspec.lock as the tool version constraint to update the artifacts.

Context

If you define a specific SDK version, e.g. flutter: 3.16.9 in pubspec.yaml, the resulted pubspec.lock would still generate a ranged version flutter: ">=3.16.9".

Right now, Renovate uses the version from the lock file to determine the tool/SDK version constraint, which might not be accurate to what's defined in pubspec.yaml. And causing the wrong version to be used to update the artifacts. For example, the current latest Flutter version is 3.19.0 which would conflict to what's defined in pubspec.yaml and may fail to update artifacts.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[HonkingGoose]

I'm happy with the PR title now. I'll let the maintainers review the code.

[renovate-release]

🎉 This PR is included in version 37.204.1 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)
• 37.204.1

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