Diversify GitHub CI build platforms: add macOS 11, Windows 2022

GitHub runners have gained support for Windows 2022 and macOS 11. Switch
some of our CI jobs to these newer platforms to make sure we detect
platform-specific issues. There remain other CI jobs on the previous
platforms (Windows 2019 and macOS 10.15, respectively).

Author: tautschnig

.github/workflows/pull-request-checks.yaml

@@ -343,8 +343,8 @@ jobs:
       - name: Run JBMC regression tests
         run: make -C jbmc/regression test-parallel JOBS=3
 
-  check-macos-10_15-cmake-clang:
-    runs-on: macos-10.15
+  check-macos-11-cmake-clang:
+    runs-on: macos-11
     steps:
       - uses: actions/checkout@v2
         with:
@@ -426,8 +426,8 @@ jobs:
           Set-Location build
           ctest -V -L CORE -C Release . -j2
 
-  check-vs-2019-make-build-and-test:
-    runs-on: windows-2019
+  check-vs-2022-make-build-and-test:
+    runs-on: windows-2022
     env:
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps: