use 1.77.2 toolchain for windows 7

Author: mxve

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
         uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: stable
+          toolchain: 1.77.2-i686-pc-windows-msvc
           target: i686-pc-windows-msvc
           override: true