Update actions/checkout action to v3

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	major	v2 -> v3

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Release Notes

actions/checkout

### [`v3`](https://togithub.com/actions/checkout/compare/v2...v3) [Compare Source](https://togithub.com/actions/checkout/compare/v2...v3)

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Configuration

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This change is 

[codecov[bot]]

Codecov Report

Merging #97 (74d6aed) into master (1d0fdd7) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #97   +/-   ##
=========================================
  Coverage     93.98%   93.98%           
- Complexity      183      187    +4     
=========================================
  Files             2        2           
  Lines           665      665           
=========================================
  Hits            625      625           
  Misses           40       40           

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[coveralls]

Coverage remained the same at 94.01% when pulling 74d6aed3348ff04c9134276329812ee7d7523a5b on renovate/actions-checkout-3.x into 1d0fdd796164f3612e0eb22f090a9f3c9a8ed40a on master.