Use apt packaged cmake version in tester

[gassmoeller]

We have some unexplained test failures in the indent tester in the compile stage (see e.g. #5560
). After some investigation I found this: It looks like the new cmake (3.28.2) version that was included in the github actions runner yesterday broke the compatibility of precompiled headers and unity builds (see discussion here). cmake 3.28.3 should fix this, but who knows when it will be released and deployed in the actions runner. Therefore this PR tries to circumvent the problem by using the apt packaged version of cmake on the runner (that we install anyway). If this works the tester should now use cmake 3.16 which comes with ubuntu 20.04. We can revert this change later.

[bangerth]

Ah, good job. I tried to understand the failure in #5560 but could not make sense of it.

[gassmoeller]

Yup, it reminded me of an earlier case we had last year, that is how I figured it out. Also it looks like it is working, the indent+documentation tester passed. Let's wait for the rest of the testers.