Update go to 1.25 across all Dockerfile definitions

[anoadragon453]

These spots were missed in #3688. Found by looking at https://github.com/element-hq/dendrite/pull/3582/changes.

I've added some comments to avoid missing this again in the future.

Recommended to review commit-by-commit.

Pull Request Checklist

• I have added Go unit tests or Complement integration tests for this PR or I have justified why this PR doesn't need tests
• Pull request includes a sign off below or I have already signed off privately

Signed-off-by: Andrew Morgan <andrewm@element.io>

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.21%. Comparing base (933a12d) to head (678a35e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3698   +/-   ##
=======================================
  Coverage   52.21%   52.21%           
=======================================
  Files         524      524           
  Lines       48435    48435           
=======================================
+ Hits        25291    25292    +1     
- Misses      19626    19628    +2     
+ Partials     3518     3515    -3     

Flag	Coverage Δ
unittests	52.21% <ø> (+<0.01%)	⬆️

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[anoadragon453]

Not much to see here, so just going to merge.

cc @richvdh who reviewed the original PR; there were other spots apparently.