Fix builds from CI showing up as modified (#4384)

This change also adds a new environment variable used while building: `CHATTERINO_REQUIRE_CLEAN_GIT` which, if set, will error out during your build's GIT stage.
This is used in CI to ensure we don't accidentally introduce a change that would result in builds showing up as "modified" again.

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

.github/workflows/build.yml

@@ -14,6 +14,7 @@ concurrency:
 
 env:
   C2_ENABLE_LTO: ${{ github.ref == 'refs/heads/master' }}
+  CHATTERINO_REQUIRE_CLEAN_GIT: On
 
 jobs:
   build:
@@ -81,9 +82,8 @@ jobs:
         uses: jurplel/install-qt-action@v3.0.0
         with:
           cache: true
-          cache-key-prefix: ${{ runner.os }}-QtCache-${{ matrix.qt-version }}
+          cache-key-prefix: ${{ runner.os }}-QtCache-${{ matrix.qt-version }}-v2
           version: ${{ matrix.qt-version }}
-          dir: "${{ github.workspace }}/qt/"
 
       # WINDOWS
       - name: Cache conan packages part 1