chore(connectivity_plus): Update Flutter dependencies, set Flutter >=3.3.0 and Dart to >=2.18.0 <4.0.0

[vbuberen]

Description

Updating used dependencies and aligning constraint with other plugins maintained by the Flutter team (for example, here: https://github.com/flutter/packages/blob/main/packages/url_launcher/url_launcher/pubspec.yaml#L8). Not marking as a breaking change as we already have namespace marked as breaking change.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.