[main] Upgrade the Golang version to go1.25.6

[vitess-bot]

This Pull Request bumps the Golang version to go1.25.6 and the bootstrap version to 50.

Do not trust the bot blindly. A thorough code review must be done to ensure all the files have been correctly modified.

There are manual steps remaining:

• Build and Push the bootstrap images to Docker Hub, the bot cannot handle that

cc @vitessio/release

[vitess-bot]

Hello! 👋

This Pull Request is now handled by arewefastyet. The current HEAD and future commits will be benchmarked.

You can find the performance comparison on the arewefastyet website.

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.92%. Comparing base (4a3e6a3) to head (6c1bc98).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19180      +/-   ##
==========================================
+ Coverage   69.91%   69.92%   +0.01%     
==========================================
  Files        1613     1611       -2     
  Lines      216122   216176      +54     
==========================================
+ Hits       151097   151162      +65     
+ Misses      65025    65014      -11     

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