ci: Enable image tests on mac

.github/workflows/test_rust.yml

@@ -79,15 +79,10 @@ jobs:
           RUSTDOCFLAGS: -D warnings
 
       - name: Run tests with image tests
-        if: runner.os == 'Linux' || runner.os == 'Windows'
         run: cargo test --locked --features imgtests
         env:
           XDG_RUNTIME_DIR: '' # dummy value, just to silence warnings about it missing
 
-      - name: Run tests without image tests
-        if: ${{ !(runner.os == 'Linux' || runner.os == 'Windows') }}
-        run: cargo test --locked
-
       - name: Upload images
         if: failure()
         uses: actions/upload-artifact@v3