ci: add FIXME for 32-bit windows-gnu msys2 problem

Author: jieyouxu

.github/workflows/ci.yml

@@ -83,6 +83,11 @@ jobs:
       - if: contains(matrix.os, 'windows')
         uses: msys2/[email protected]
         with:
+          # FIXME(#136795): this mingw installation seems to be needed for
+          # `i686-pc-windows-gnu`, otherwise we somehow incorrectly link to
+          # 64-bit `libwinpthread-1.dll` and then `rustc` can't find the 32-bit
+          # version it wants.
+          #
           # i686 jobs use mingw32. x86_64 and cross-compile jobs use mingw64.
           msystem: ${{ contains(matrix.name, 'i686') && 'mingw32' || 'mingw64' }}
           # don't try to download updates for already installed packages