ci: Pin the nightly toolchain for i686-pc-windows-gnu

Pin i686-pc-windows-gnu to nightly-2025-02-07 until [1] is resolved.

[1]: rust-lang#136795

Author: tgross35

library/compiler-builtins/.github/workflows/main.yml

@@ -98,7 +98,8 @@ jobs:
           test_verbatim: 1
         - target: i686-pc-windows-gnu
           os: windows-latest
-          rust: nightly-i686-gnu
+          # FIXME: pinned due to https://github.com/rust-lang/rust/issues/136795
+          rust: nightly-2025-02-07-i686-gnu
         - target: x86_64-pc-windows-gnu
           os: windows-latest
           rust: nightly-x86_64-gnu