Build failure with Meson >= 1.8.3 on Windows

I recently tried to update the version of Meson used in my winpgbuild project, which builds PostgreSQL for Windows, along with (almost) all the various dependencies. Something has changed in versions from 1.8.3 and above which causes the regression tests to fail:

This successful run is with Meson 1.8.2: https://github.com/dpage/winpgbuild/actions/runs/18462942864

This failed run is with Meson 1.8.3: https://github.com/dpage/winpgbuild/actions/runs/18464267466

This failed run is with Meson 1.8.5: https://github.com/dpage/winpgbuild/actions/runs/18456020620

Logs etc. can be found at the URLs above (you might need to be logged into Github to see them); I haven't attached them here as they will almost certainly exceed the size limit for the mailing list.

We do have 3 build farm animals running Meson, however they all have significantly older versions installed.