CI: patch pip to fix issue with Homebrew Python

See pypa/pip#11598.

Author: dnicolodi

.github/workflows/tests.yml

@@ -205,6 +205,18 @@ jobs:
           brew install --overwrite python@${{ matrix.python }}
           echo /usr/local/opt/python@${{ matrix.python }}/libexec/bin/ >> $GITHUB_PATH
 
+      - name: Patch pip
+        # Patch https://github.com/pypa/pip/issues/11539
+        run: |
+          cat >>/usr/local/lib/python${{ matrix.python }}/site-packages/pip/_internal/locations/_sysconfig.py <<EOF
+          def get_prefixed_libs(prefix: str) -> typing.Tuple[str, str]:
+              if "venv" in sysconfig.get_scheme_names():
+                  paths = sysconfig.get_paths(vars={"base": prefix, "platbase": prefix}, scheme="venv")
+              else:
+                  paths = sysconfig.get_paths(vars={"base": prefix, "platbase": prefix})
+              return (paths["purelib"], paths["platlib"])
+          EOF
+
       - name: Install
         run: python -m pip --disable-pip-version-check install .[test]