7238: Point to CoC which contains the contributor covenant r=deivid-rodriguez a=ajwann

### What was the end-user problem that led to this PR?

The generated README contains two different links to contributor covenant. Since the generated Code of Conduct *contains* the text of the Contributor Covenant, we can just point the generated README to the generated CoC, and explicitly refer to it as the code of conduct. 

### What is your fix for the problem, implemented in this PR?

The generated readme now points to the gems CoC (which contains the Contributor Covenant)

Closes #6905.

Co-authored-by: Adam Wanninger <ajwann@ajwann.com>

7255: Improve environment backup and restore r=hsbt a=deivid-rodriguez

### What was the end-user problem that led to this PR?

The problem was that the specs were removing some environment variables for every tests, but not all of them, causing problems on some environments (see #7251).

### What was your diagnosis of the problem?

My diagnosis was that we don't really need to do this.

### What is your fix for the problem, implemented in this PR?

My fix is to stop doing it, and fix the very few specs that failed after the change. One of the failures actually led to a bug fix (I think), see 6c27ebb.

### Why did you choose this fix out of the possible options?

I chose this fix because I think it's cleaner than adding a public constant in `lib/` only to fix a problem with the specs, like it's done in #7251.


Co-authored-by: David Rodríguez <deivid.rodriguez@riseup.net>