ci: Try to fix job which is killed due to low memory?

[piponazo]

As we discussed in the team chat, I am trying to fix the Debug+Coverage jobs which runs on PUSH on the main branch every time we merge a PR:
https://github.com/Exiv2/exiv2/actions/workflows/on_push_ExtraJobsForMain.yml

These jobs fail with this error:

[ 75%] Building CXX object samples/CMakeFiles/conntest.dir/conntest.cpp.o
[ 75%] Building CXX object samples/CMakeFiles/remotetest.dir/remotetest.cpp.o
c++: fatal error: Killed signal terminated program cc1plus
compilation terminated.

And we think it might be caused by the job running out of RAM memory. It is weird but the same jobs runs perfectly fine on PRs. The specs of the runners used by Github can be found here:
https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources

In this experiment we are trying to remove the --parallel flag to compile the project just with 1 single core.

[codecov]

Codecov Report

Merging #2185 (2be613e) into main (74622cf) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2185      +/-   ##
==========================================
- Coverage   63.30%   63.29%   -0.02%     
==========================================
  Files          99       99              
  Lines       19596    19596              
  Branches     9559     9559              
==========================================
- Hits        12406    12404       -2     
- Misses       5116     5118       +2     
  Partials     2074     2074              

Impacted Files	Coverage Δ
src/xmp.cpp	76.44% <0.00%> (-0.40%)	⬇️

---

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[piponazo]

It seems that it worked out! 😁