Use same CMake minimum version in DownloadProject configuration

[tautschnig]

We already have a top-level minimum requirement for CMake >= 3.8, so don't need to specify a lower requirement in a file included from the top level.

Having a requirement as low as 2.8.2 broke building on newer version of CMake, which error with "Compatibility with CMake < 3.5 has been removed from CMake." (seen in GitHub runners with Ubuntu 24.04).

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[tautschnig]

FWIW: https://github.com/model-checking/kani/actions/runs/14191553578/job/39757217581#step:5:55 is an example of such a failing build attempt.

[TGWDB]

We already have a top-level minimum requirement for CMake >= 3.8, so don't need to specify a lower requirement in a file included from the top level.

If we have a top level requirement why are we (re)specifying the requirement somewhere else? (Not a blocker, but seems a bit odd.)

[tautschnig]

If we have a top level requirement why are we (re)specifying the requirement somewhere else? (Not a blocker, but seems a bit odd.)

That is what I thought as well (and tried the first time around), but then it seems that the use of project in that file requires that cmake_minimum_version be specified in the same file.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.63%. Comparing base (cd39b3a) to head (6cbc63b).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #8611    +/-   ##
=========================================
  Coverage    79.63%   79.63%            
=========================================
  Files         1733     1733            
  Lines       197820   197820            
  Branches     18173    17968   -205     
=========================================
+ Hits        157536   157537     +1     
+ Misses       40284    40283     -1     

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