A line in Proj6 may corrupt Proj3 randomly

[johnhaxx7]

---

Env setup
Go: 1.16
Current progress: proj3 in progress, proj1&2 fin

---

When I test my code for as the the last section in this page:
https://github.com/tidb-incubator/tinysql/blob/course/courses/proj3-README-zh_CN.md

I hit this line sometimes:
https://github.com/tidb-incubator/tinysql/blob/1bdb9a3bc6ba158424a7da352d14d2b72d39ebaf/store/tikv/snapshot.go#L150

After I commented it out, those tests are able to pass.

Can someone please check if that's a real issue or a bug introduced by my change?