bpo-30602: Fix refleak in os.spawnv() (#2212) (#2486)

When os.spawnv() fails while handling arguments, free correctly
argvlist: pass lastarg+1 rather than lastarg to free_string_array()
to also free the first item.
(cherry picked from commit 8acb4cf2b3436652568d7a70228b166316181466)
1 file changed