Fix test_render_all_run_gallery_invokes_subprocess clobbering LaTeX's own subprocess.run

render_mod.subprocess is the stdlib subprocess module itself, not a copy —
patching .run unconditionally also intercepted the real subprocess.run
calls matplotlib's texmanager makes to compile LaTeX during savefig, so
those returned the test's fake return value instead of a real
CompletedProcess and crashed with AttributeError: 'NoneType' object has no
attribute 'stdout' on any environment where render_all runs before the
gallery call (i.e. everywhere but this dev machine's warm state that
happened to mask it). Only intercept the "gallery generate" call now;
everything else passes through to the real subprocess.run.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_render.py

@@ -98,10 +98,21 @@ def test_render_router_diagnostics_and_edge_cases(tmp_path: Path):
 
 
 def test_render_all_run_gallery_invokes_subprocess(tmp_path: Path, monkeypatch):
+    # render_mod.subprocess *is* the stdlib subprocess module, so a blanket
+    # patch of .run would also swallow the real subprocess.run calls
+    # matplotlib's texmanager makes to compile LaTeX during savefig — only
+    # intercept the "gallery generate" call itself and pass everything else
+    # (LaTeX included) through to the real subprocess.run.
     calls = []
-    monkeypatch.setattr(
-        render_mod.subprocess, "run", lambda *a, **k: calls.append((a, k))
-    )
+    real_run = render_mod.subprocess.run
+
+    def fake_run(*a, **k):
+        if a and a[0] and a[0][0] == "gallery":
+            calls.append((a, k))
+            return None
+        return real_run(*a, **k)
+
+    monkeypatch.setattr(render_mod.subprocess, "run", fake_run)
     reduced = [
         Reduced(
             "s",