Warn if merge commit content differs to branch head

[IanButterworth]

This branch is intentionally one commit behind main to demo it.

https://github.com/julia-actions/julia-runtest/actions/runs/19194942443/job/54874512012?pr=152#step:8:223

│
│ To reproduce this CI run locally run the following from the same repository state on julia version 1.12.1:
│
│ `import Pkg; Pkg.test(;coverage=true, julia_args=["--check-bounds=yes", "--compiled-modules=yes", "--depwarn=yes"], force_latest_compatible_version=false, allow_reresolve=true)`
│
│ Note: This is being run on merge commit 137b87f24bd7e4d5979b3d8260e78b0472db300e (merge of PR branch 'ib/warn_git' into 'main').
│ The content differs from the actual commit on your PR branch.
│ To reproduce locally, update your branch with 'main' first.
│

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a3f3749) to head (6000c9b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #152   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines            2         2           
=========================================
  Hits             2         2           

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