fix: memory-leak in .transaction()

[Uzlopak]

#11256

[Uzlopak]

When I apply my patch, the sessions wont leak anymore

~/Workspace/session-leak$ node --inspect main.js 
Debugger listening on ws://127.0.0.1:9229/579962f1-ca8b-4c2d-b279-e1ce54d6dbad
For help, see: https://nodejs.org/en/docs/inspector
2022-01-24T03:21:55.906Z sessions = 0
2022-01-24T03:21:56.925Z sessions = 0
2022-01-24T03:21:57.940Z sessions = 0
2022-01-24T03:21:58.957Z sessions = 0

Also mongodb-team describes it self:

https://www.mongodb.com/blog/post/quick-start-nodejs--mongodb--how-to-implement-transactions

Regardless of what happens, we need to end our session.

[vkarpov15]

Good catch, thanks 👍