CI: Include CMakeLists.txt in the cache

> CMake is re-running because D:/a/VVVVVV/VVVVVV/desktop_version
> /build_default/CMakeFiles/generate.stamp is out-of-date.
>   the file 'D:/a/VVVVVV/VVVVVV/desktop_version/CMakeLists.txt'
>   is newer than 'D:/a/VVVVVV/VVVVVV/desktop_version/build_default
>   /CMakeFiles/generate.stamp.depend'
>   result='-1'

"newer" probably means "the last edit date is newer because it was just
cloned", so let's see if including it in the cache means the last edit
date will be kept the same too... We can freely do this, as the cache
key includes the hash of the file itself.

.github/workflows/ci.yml

@@ -145,7 +145,9 @@ jobs:
       env:
         cache-name: cache-windows-build-folder-VS2022
       with:
-        path: desktop_version/build
+        path: |
+          desktop_version/build
+          desktop_version/CMakeLists.txt
         key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('desktop_version/CMakeLists.txt') }}-SDL${{ env.SDL_VERSION }}
 
     - if: ${{ steps.cache-windows-build-folder.outputs.cache-hit != 'true' }}