Add should skip check to build

[calumy]

Add a condition to check if the global should skip result is true before evaluating stage conditions.

Snippet from fkirc/skip-duplicate-actions docs.

    # If 'skip-duplicate-actions' terminates before the paths checks are performed (for example, when a successful duplicate run has
    # been found) 'paths_result' outputs an empty object ('{}'). This can be easily intercepted in the if condition of a job
    # by checking the result of the "global" 'should_skip' output first.