run_context: add GITHUB_RUN_ATTEMPT (#2458)

* run_context: add GITHUB_RUN_ATTEMPT

Fixes https://github.com/nektos/act/issues/2451
Fixes https://github.com/nektos/act/issues/1615

* fix whitespace

* fix githubcontext

* fix TestSetupEnv

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Co-authored-by: ChristopherHX <christopher.homberger@web.de>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>