Momentarily downgrade Git on Cygwin to investigate failures

Using this older version is not in general secure, since the new version is a security update. It is sometimes acceptable to run software with security bugs in CI workflows, but the intent of this change is just to check if the version of the Cygwin `git` package is the cause of the failures. If so, they can probably be fixed or worked around in a better way than downgrading. (Furthermore, the lower version of the `git` package will not always be avaialable from Cygwin's repositories.)

Author: EliahKagan

.github/workflows/cygwin-test.yml

@@ -30,7 +30,7 @@ jobs:
  - name: Set up Cygwin
 uses: egor-tensin/setup-cygwin@v4
 with:
-packages: python39=3.9.16-1 python39-pip python39-virtualenv git
+packages: python39=3.9.16-1 python39-pip python39-virtualenv git=2.43.0-1
 
  - name: Arrange for verbose output
 run: |