Do not run CI for all Go versions and use caching

[rdimitrov]

The following PR:

• Removes the tests we were running against all available Go versions above the one we are using in the go.mod file. This sounded useful, but it caused more CI failures than it helps.
• Sets the cache: true for most go actions

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.18%. Comparing base (85bd220) to head (decacdd).
Report is 29 commits behind head on master.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #606   +/-   ##
=======================================
  Coverage   70.18%   70.18%           
=======================================
  Files          10       10           
  Lines        2123     2123           
=======================================
  Hits         1490     1490           
  Misses        517      517           
  Partials      116      116           

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[kommendorkapten]

Looks good, is the windows tests expected to fail?

[rdimitrov]

Looks good, is the windows tests expected to fail?

@kommendorkapten - Yes, they were disabled before, but once we enabled them we saw there're a few issues when targets use the prefixed format we use in the tuf-demo repo.

I've opened an issue, but from what I see it's probably caused by the wrong handling of back/forward slashes when we are translating a target name to a local path name when we create or look for the target file locally.

I don't have a windows machine to properly debug and fix this, so I thought it's better to leave the tests enabled and failing until we get some help on this. Also this way we are open in sharing windows support is not working properly yet.