[CI] Update Github action versions, cache pip

[f-dangel]

Minor maintenance that speeds up the GH action installations.

[coveralls]

Pull Request Test Coverage Report for Build 10966688702

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.021%

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Totals
Change from base Build 10966654871:	0.0%
Covered Lines:	1346
Relevant Lines:	1512

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💛 - Coveralls