Update apt repositories before installing dependencies

[speth]

This should fix some transient CI failures (e.g. #995) when package versions are removed from the remote repositories.

Changes proposed in this pull request

• Run apt update before apt install ...

If applicable, fill in the issue number this pull request is fixing

Closes #1055

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

Merging #1056 (2d99eb5) into main (01bf417) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 2d99eb5 differs from pull request most recent head a1cd9cd. Consider uploading reports for the commit a1cd9cd to get more accurate results

@@           Coverage Diff           @@
##             main    #1056   +/-   ##
=======================================
  Coverage   72.59%   72.60%           
=======================================
  Files         356      356           
  Lines       46508    46508           
=======================================
+ Hits        33763    33765    +2     
+ Misses      12745    12743    -2     

Impacted Files	Coverage Δ
src/base/AnyMap.cpp	89.61% <0.00%> (+0.20%)	⬆️

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[ischoegl]

Looks good to me.