gh-37010: src/tox.ini (coverage:run): Set `concurrency = multiproce…

…ssing,threads`

    
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URL: #37010
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee

src/tox.ini

@@ -388,7 +388,7 @@ consider_namespace_packages = True
 
 [coverage:run]
 source = sage
-concurrency = multiprocessing
+concurrency = multiprocessing,thread
 data_file = .coverage/.coverage
 disable_warnings = no-data-collected