Freeze Windows runner version

Author: skirpichev

.github/workflows/pip_install_gmpy2.yml

@@ -85,7 +85,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [windows-latest]
+        os: [windows-2022]
     runs-on: ${{ matrix.os }}
     defaults:
       run: