Handle multiple paths in appdirs.site_config_dirs on MacOS (#13280)

This occurs when using Homebrew, for example.

Author: alexreg

news/12903.bugfix.rst

@@ -0,0 +1 @@
+Support multiple global configuration paths returned by ``platformdirs`` on MacOS.

src/pip/_internal/utils/appdirs.py

@@ -42,7 +42,8 @@ def user_config_dir(appname: str, roaming: bool = True) -> str:
 # see <https://github.com/pypa/pip/issues/1733>
 def site_config_dirs(appname: str) -> List[str]:
     if sys.platform == "darwin":
-        return [_appdirs.site_data_dir(appname, appauthor=False, multipath=True)]
+        dirval = _appdirs.site_data_dir(appname, appauthor=False, multipath=True)
+        return dirval.split(os.pathsep)
 
     dirval = _appdirs.site_config_dir(appname, appauthor=False, multipath=True)
     if sys.platform == "win32":

tests/unit/test_appdirs.py

@@ -109,6 +109,17 @@ def test_site_config_dirs_osx(self, monkeypatch: pytest.MonkeyPatch) -> None:
             "/Library/Application Support/pip",
         ]
 
+    @pytest.mark.skipif(sys.platform != "darwin", reason="MacOS-only test")
+    def test_site_config_dirs_osx_homebrew(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        monkeypatch.setattr(sys, "prefix", "/opt/homebrew/")
+
+        assert appdirs.site_config_dirs("pip") == [
+            "/opt/homebrew/share/pip",
+            "/Library/Application Support/pip",
+        ]
+
     @pytest.mark.skipif(sys.platform != "linux", reason="Linux-only test")
     def test_site_config_dirs_linux(self, monkeypatch: pytest.MonkeyPatch) -> None:
         monkeypatch.delenv("XDG_CONFIG_DIRS", raising=False)