CI: downgrade .NET tests to macOS 13 (required for older runtimes)

Author: ForNeVeR

.github/workflows/build-rd-net.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ macos-14, ubuntu-22.04, windows-2022 ]
+        os: [ macos-13, ubuntu-22.04, windows-2022 ]
       fail-fast: false
     timeout-minutes: 15
     steps: