Updated capitalisation

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

Tests/test_file_libtiff.py

@@ -185,7 +185,7 @@ def test_write_metadata(self, tmp_path):
             for field in requested_fields:
                 assert field in reloaded, f"{field} not in metadata"
 
-    @pytest.mark.valgrind_known_error(reason="Known Invalid Metadata")
+    @pytest.mark.valgrind_known_error(reason="Known invalid metadata")
     def test_additional_metadata(self, tmp_path):
         # these should not crash. Seriously dummy data, most of it doesn't make
         # any sense, so we're running up against limits where we're asking