Fix a leak in evp_test

If evp_test fails to load the legacy provider then it leaks a reference
to the default provider.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9270)

test/evp_test.c

@@ -3096,8 +3096,10 @@ int setup_tests(void)
         return 0;
 #ifndef NO_LEGACY_MODULE
     legacyprov = OSSL_PROVIDER_load(NULL, "legacy");
-    if (!TEST_ptr(legacyprov))
+    if (!TEST_ptr(legacyprov)) {
+        OSSL_PROVIDER_unload(defltprov);
         return 0;
+    }
 #endif /* NO_LEGACY_MODULE */
 
     ADD_ALL_TESTS(run_file_tests, n);