Workflow improvements and code quality passing

[jeroenlammersma]

Description

• Corrected name of unit tests workflow to 'Unit Tests' (was 'Static Code Analysis')
• Updated checkout actions to v3.
• Made some small tweaks to ensure 'Check Code Quality with Pylint' job passes.

Where has this been tested?

• Platform(s): 20.04
• Python version(s): 3.8.10
• Unreal Engine version(s): UE4
• CARLA version: 0.9.15

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This change is 

[glopezdiest]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @jeroenlammersma)