Merge pull request #2007 from EliahKagan/cygwin-py39-venv

Work around Cygwin CI failure #2004, except for `test_installation`

.github/workflows/cygwin-test.yml

@@ -15,7 +15,7 @@ jobs:
 
     defaults:
       run:
-        shell: C:\tools\cygwin\bin\bash.exe --login --norc -eo pipefail -o igncr "{0}"
+        shell: C:\cygwin\bin\bash.exe --login --norc -eo pipefail -o igncr "{0}"
 
     steps:
     - name: Force LF line endings
@@ -27,10 +27,11 @@ jobs:
       with:
         fetch-depth: 0
 
-    - name: Set up Cygwin
-      uses: egor-tensin/setup-cygwin@v4
+    - name: Install Cygwin
+      uses: cygwin/cygwin-install-action@v5
       with:
-        packages: python39 python39-pip python39-virtualenv git
+        packages: python39 python39-pip python39-virtualenv git wget
+        add-to-path: false  # No need to change $PATH outside the Cygwin environment.
 
     - name: Arrange for verbose output
       run: |
@@ -57,9 +58,13 @@ jobs:
 
     - name: Set up virtualenv
       run: |
-        python -m venv .venv
+        python3.9 -m venv --without-pip .venv
         echo 'BASH_ENV=.venv/bin/activate' >>"$GITHUB_ENV"
 
+    - name: Bootstrap pip in virtualenv
+      run: |
+        wget -qO- https://bootstrap.pypa.io/get-pip.py | python
+
     - name: Update PyPA packages
       run: |
         # Get the latest pip, wheel, and prior to Python 3.12, setuptools.