The [skip ci] option shouldn't count as CIRRUS_LAST_GREEN_CHANGE

[leshik]

Description

Don't use git commit sha for the CIRRUS_LAST_GREEN_CHANGE env variable if [skip ci] option was used.

Context

Right now it's possible to work around the failed build by just updating e.g. README.md, and setting [skip ci] in the commit message. This breaks setups that use the CIRRUS_LAST_GREEN_CHANGE env to e.g. lint only changed files, or in case the suite is skipped completely if there are no changes to some specific files.

[fkorotkov]

Skipped builds should be ignored now while calculating last green build.