Fix a typo in DBSSTTest.DBWithMaxSpaceAllowedWithBlobFiles (#9270)

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/9270

Test Plan:
```
gtest-parallel --repeat=10000 ./db_sst_test --gtest_filter=DBSSTTest.DBWithMaxSpaceAllowedWithBlobFiles
```

Reviewed By: akankshamahajan15

Differential Revision: D32958154

Pulled By: ltamasi

fbshipit-source-id: b6ec2fbbece80d73c567cec57638dffd3c84a2ba

db/db_sst_test.cc

@@ -1099,7 +1099,7 @@ TEST_F(DBSSTTest, DBWithMaxSpaceAllowedWithBlobFiles) {
   ASSERT_EQ(sfm->GetTotalSize(), total_files_size);
 
   // Set the maximum allowed space usage to the current total size.
-  sfm->SetMaxAllowedSpaceUsage(files_size + 1);
+  sfm->SetMaxAllowedSpaceUsage(total_files_size + 1);
 
   bool max_allowed_space_reached = false;
   bool delete_blob_file = false;