Ensure q variable is freed

Fixes: d88c43a644 ("Ensure that empty or 1 element stacks are always sorted.")
Resolves: https://scan5.scan.coverity.com/#/project-view/65138/10222?selectedIssue=1665465
Signed-off-by: Nikola Pajkovsky <nikolap@openssl.org>

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28596)

test/stack_test.c

@@ -321,6 +321,7 @@ static int test_uchar_stack(int reserve)
 end:
     sk_uchar_free(r);
     sk_uchar_free(s);
+    sk_uchar_free(q);
     return testresult;
 }