TST: Fix test_pickle_load_from_subprocess in a dirty tree

For a ditry tree, `setuptools-scm` adds the date to the end of the
version. This test runs a subprocess and `subprocess_run_helper` will
set `SOURCE_DATE_EPOCH=0`, which forces the date to be 1970-01-01,
triggering a mismatched version warning on unpickle.

Since we aren't testing the version-compatibility warning, set
`SETUPTOOLS_SCM_PRETEND_VERSION_FOR_MATPLOTLIB` in the subprocess call
so that versions match.

Also, set the `dist_name` parameter when querying setuptools-scm or it
won't check that environment variable.

Author: QuLogic

lib/matplotlib/__init__.py

@@ -225,6 +225,7 @@ def _get_version():
         else:
             return setuptools_scm.get_version(
                 root=root,
+                dist_name="matplotlib",
                 version_scheme="release-branch-semver",
                 local_scheme="node-and-date",
                 fallback_version=_version.version,

lib/matplotlib/tests/test_pickle.py

@@ -150,7 +150,15 @@ def test_pickle_load_from_subprocess(fig_test, fig_ref, tmp_path):
     proc = subprocess_run_helper(
         _pickle_load_subprocess,
         timeout=60,
-        extra_env={'PICKLE_FILE_PATH': str(fp), 'MPLBACKEND': 'Agg'}
+        extra_env={
+            "PICKLE_FILE_PATH": str(fp),
+            "MPLBACKEND": "Agg",
+            # subprocess_run_helper will set SOURCE_DATE_EPOCH=0, so for a dirty tree,
+            # the version will have the date 19700101. As we aren't trying to test the
+            # version compatibility warning, force setuptools-scm to use the same
+            # version as us.
+            "SETUPTOOLS_SCM_PRETEND_VERSION_FOR_MATPLOTLIB": mpl.__version__,
+        },
     )
 
     loaded_fig = pickle.loads(ast.literal_eval(proc.stdout))