Set up Cygwin before cloning our repo

Otherwise different Gits set up and tear down the repo,
leading to issues.

.github/workflows/testing.yml

@@ -324,8 +324,6 @@ jobs:
     runs-on: windows-2022
     timeout-minutes: 30
     steps:
-      - name: Checkout repo
-        uses: actions/checkout@v6
       - name: Setup Cygwin
         uses: cygwin/cygwin-install-action@v6
         with:
@@ -337,6 +335,8 @@ jobs:
             libpng-devel
             make
             pkg-config
+      - name: Checkout repo
+        uses: actions/checkout@v6
       - name: Build & install using Make
         shell: C:\cygwin\bin\env.exe CYGWIN_NOWINPATH=1 CHERE_INVOKING=1 C:\cygwin\bin\bash.exe -o igncr '{0}'
         run: | # Cygwin does not support `make develop` sanitizers ASan or UBSan