update test workflow to ubuntu 20.04

[ad-astra-video]

What does this pull request do? Explain your changes. (required)
Updates test workflow to use ubuntu 20.04

Specific updates (required)

• bumped ubuntu version to 20.04
• used Dockerfile to update installation steps
• removed folders not needed to create space on runner

How did you test each of these updates (required)
Ran on my fork of go-livepeer https://github.com/ad-astra-video/go-livepeer/actions/runs/5887219287

Does this pull request close any open issues?
No

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[hjpotter92]

perhaps we should also consider bumping our build pipeline to ubuntu 20 (or 22?)! wdyt @leszko / @thomshutt
https://github.com/livepeer/go-livepeer/blob/master/.github/workflows/build.yaml#L19-L20

[hjpotter92]

in my experience, github workflows work better if instead of export, we do one of:

echo TZ=Etc/UTC >> $GITHUB_ENV

or specify it in the job itself:

env:
  TZ: "Etc/UTC"

[ad-astra-video]

I have "fixed" this by removing it as part of a larger change to moving from ubuntu-latest with ubuntu:18.04 container specified to using runs-on: ubuntu-20.04.

[codecov]

Codecov Report

Merging #2841 (db0421f) into master (3f62408) will decrease coverage by 0.01567%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##              master       #2841         +/-   ##
===================================================
- Coverage   56.72881%   56.71314%   -0.01567%     
===================================================
  Files             88          88                 
  Lines          19149       19149                 
===================================================
- Hits           10863       10860          -3     
- Misses          7690        7693          +3     
  Partials         596         596                 

see 1 file with indirect coverage changes

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see 1 file with indirect coverage changes

[thomshutt]

perhaps we should also consider bumping our build pipeline to ubuntu 20 (or 22?)! wdyt @leszko / @thomshutt
https://github.com/livepeer/go-livepeer/blob/master/.github/workflows/build.yaml#L19-L20

If it's not too much work then definitely!

[hjpotter92]

hey @ad-astra-video ; i've created a new PR which bumps our ubuntu versions for build workflow as well: #2846

i've forked off from your branch! closing this PR in favour of that one.

thanks for your contribution