Cache dockerhub images from linux for macOS

[ChristopherHX]

An attempt to avoid hitting the dockerhub Pull Rate Limit.

There is a small overhead due to caching (ca. +2 min, next run within 7 days only some seconds), but it might avoid rerunning the macOS job due to this error.
Restoreing the cache doesn't take much extra job execution time, because the test step is pulling less images from dockerhub.

This PR failed due to this limit #776.
It seems to be triggered by multiple PR's are opened within some days.

Needs more testing, if this solves the dockerhub limit problems or only delays the problem to happen less frequently.

Add new dockerhub images to CACHED_DOCKER_IMAGES and increment the cache key (CACHED_DOCKER_IMAGES_KEY)

What do you think?

I need ACT_OWNER: ${{ github.repository_owner }} and ACT_REPOSITORY: ${{ github.repository }} to have all tests green within my fork

[codecov]

Codecov Report

Merging #768 (2894487) into master (0f04942) will increase coverage by 4.65%.
The diff coverage is 62.61%.

@@            Coverage Diff             @@
##           master     #768      +/-   ##
==========================================
+ Coverage   49.27%   53.92%   +4.65%     
==========================================
  Files          23       23              
  Lines        2401     2674     +273     
==========================================
+ Hits         1183     1442     +259     
+ Misses       1090     1086       -4     
- Partials      128      146      +18     

Impacted Files	Coverage Δ
pkg/container/docker_build.go	0.00% <0.00%> (ø)
pkg/container/docker_run.go	1.77% <0.00%> (-0.16%)	⬇️
pkg/common/git.go	52.85% <30.15%> (-6.94%)	⬇️
pkg/runner/runner.go	68.96% <33.33%> (-7.51%)	⬇️
pkg/model/planner.go	52.14% <43.33%> (+19.06%)	⬆️
pkg/model/workflow.go	51.08% <62.68%> (+25.37%)	⬆️
pkg/container/docker_pull.go	36.17% <64.70%> (+17.98%)	⬆️
pkg/runner/expression.go	85.38% <71.87%> (-1.26%)	⬇️
pkg/runner/step_context.go	78.92% <79.90%> (+9.97%)	⬆️
pkg/runner/run_context.go	80.36% <98.55%> (+3.95%)	⬆️
... and 7 more

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[catthehacker]

My plans are to escape DockerHub and move everything to other registries but this will suffice for now.

[ChristopherHX]

This PR doesn't need work, it only needs to be merged manually
However mergify added this label weeks later, once another PR was merged