CI: Only fetch in actions/checkout

I had the workflow fetch the repository in two steps earlier.  That was failing after the switch from egor-tensin/install-cygwin to cygwin/install-cygwin-action.  This avoids that step and hopefully sidesteps whatever the problem is; I'm hoping the problem is just internet access by an untrusted binary.

.github/workflows/cygwin.yml

@@ -24,7 +24,7 @@ jobs:
       - uses: actions/checkout@v3
         with:
           submodules: recursive
-          fetch-depth: 3000
+          fetch-depth: 0
       - name: Install Cygwin
         uses: cygwin/cygwin-install-action@v2
         with:
@@ -50,11 +50,9 @@ jobs:
         run: |
           command bash
           bash -c "uname -svrmo"
-      - name: Update with Cygwin git
-        # fetch-depth=0 above should make this short.
+      - name: Tell Cygwin's git about this repository.
         run: |
           dash -c "which git; /usr/bin/git config --system --add safe.directory /cygdrive/d/a/numpy/numpy"
-          dash -c "which git; /usr/bin/git fetch --all -p"
       - name: Verify python version
         # Make sure it's the Cygwin one, not a Windows one
         run: |