docs: reinstate artifact generation for PRs

[Habbie]

Short description

This got removed in #14767 by accident.

I tested that this works without any variables or secrets by pushing to master on a fork, without this patch.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master

[miodvallat]

I'm sure this can't make anything worse. 🤞🏻

[coveralls]

Pull Request Test Coverage Report for Build 13442483538

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 29 unchanged lines in 9 files lost coverage.
• Overall coverage increased (+3.8%) to 64.505%

---

Files with Coverage Reduction	New Missed Lines	%
ext/json11/json11.cpp	2	62.72%
modules/lmdbbackend/lmdbbackend.cc	2	73.86%
pdns/opensslsigners.cc	2	61.0%
pdns/recursordist/rec-main.cc	2	48.67%
pdns/iputils.cc	3	55.76%
pdns/recursordist/syncres.cc	3	75.71%
pdns/misc.cc	4	61.8%
pdns/recursordist/aggressive_nsec.cc	5	64.91%
pdns/dnsdistdist/dnsdist-carbon.cc	6	61.7%

Totals
Change from base Build 13433765276:	3.8%
Covered Lines:	127653
Relevant Lines:	166895

---

💛 - Coveralls