obs-scripting: Fix compiler warnings

* obs-scripting: Fix unused 'varargs' warning

* obs-scripting: Fix PyEval deprecation warnings
Remove PyEval_InitThreads() and PyEval_ThreadsInitialized() call for
Python 3.7 and later as Python calls it automatically now.

This removes deprecation warnings when using Python 3.9 or later.

https://docs.python.org/3/c-api/init.html#c.PyEval_InitThreads

deps/obs-scripting/obs-scripting-python.c

@@ -1644,9 +1644,11 @@ bool obs_scripting_load_python(const char *python_path)
 	dstr_free(&old_path);
 #endif
 
+#if PY_VERSION_HEX < 0x03070000
 	PyEval_InitThreads();
 	if (!PyEval_ThreadsInitialized())
 		return false;
+#endif
 
 	/* ---------------------------------------------- */
 	/* Must set arguments for guis to work            */