RUNNER_ARCH is not defined

[datosh]

Act version

act version 0.2.30

Feature description

GitHub added a runner context variable called runner.arch.

Just as https://github.com/nektos/act/issues/171 added support for runner.os I would like to have support for runner.arch in act so that I can use actions like Sigstore that use these values.

[datosh]

PR: #1290

[ChristopherHX]

This issue wasn't auto closed by the PR, it is released in 0.2.31