Don't activate version on build

[stsewd]

Close #4793

I was trying to write a test for this, but is so complicated or I don't know how
to do it, as it requires to hit the api from the SLUMBER setting.

I was trying using live server, but it didn't work as expected... If codecov fails,
at least I could test that we are calling to the patch with built=True

[codecov]

Codecov Report

Merging #4810 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4810   +/-   ##
=======================================
  Coverage   76.26%   76.26%           
=======================================
  Files         158      158           
  Lines       10034    10034           
  Branches     1267     1267           
=======================================
  Hits         7652     7652           
  Misses       2039     2039           
  Partials      343      343

Impacted Files	Coverage Δ
readthedocs/projects/tasks.py	69.51% <ø> (ø)	⬆️

[stsewd]

Also, this isn't a replacement of #4733, as that PR is needed to not build inactive versions via webhooks

[humitos]

I know there are different opinions here, but I'm fine by merging this PR.

Although that building a version without making it active doesn't make too much sense for the service, I think that making it automatically makes things to be confusing (as we were confused when working on #4733 and #4810

Also, this could allow us to run management commands to build versions without publishing them, etc.

I only see "positive" things with this change and no negative ones.

[ericholscher]

I'm willing to test this, but it feels like we're solving a symptom instead of a root cause. I'm also guessing we're going to hit issues with people building docs, and not having them become active, but those will also be bugs, and should be simple to solve.