[draft] Improve keyboard shortcut hint text in GitHub Sync Modal

[lmac-1]

Update the hint text to clarify that Ctrl+Enter (or Cmd+Enter) should be pressed while typing in the commit message textarea. The previous text was ambiguous about when to use the shortcut. Also update the corresponding test to match the new hint text.

Closes #4315

Validation steps

1. Go to a workflow with GitHub integrated
2. Click the chevron icon next to Save and click "Save & Sync"
3. Observe the "Tip" help text

Additional notes for the reviewer

1. When I raised the issue, I thought that the keyboard shortcut was incorrect and that it should refer to the shortcut for Save + Sync (Mod + Shift + S). When implementing and looking at the GitHubSyncModal test, I realised that the keyboard shortcut was correct - it's just that it only works when you are inside the commit message text box. Open to suggestions for better wording.

AI Usage

Please disclose whether you've used AI anywhere in this PR (it's cool, we just
want to know!):

• I have used Claude Code
• I have used another model
• I have not used AI

You can read more details in our
Responsible AI Policy

Pre-submission checklist

• I have performed an AI review of my code (we recommend using /review
  with Claude Code)
• I have implemented and tested all related authorization policies.
  (e.g., :owner, :admin, :editor, :viewer)
• I have updated the changelog.
• I have ticked a box in "AI usage" in this PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.34%. Comparing base (bf124d7) to head (965e8c0).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4330      +/-   ##
==========================================
+ Coverage   89.30%   89.34%   +0.04%     
==========================================
  Files         425      425              
  Lines       19979    19979              
==========================================
+ Hits        17842    17851       +9     
+ Misses       2137     2128       -9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[lmac-1]

Closing as we will keep the help text as is. It's correct when someone is in the textarea.