Fix unexecuted CWL jobs with dynamic requirements failing on missing inputs

[adamnovak]

This will fix #4930 by patching a hole where we could run fill_in_defaults() for a CWL job's inputs before checking that its conditional was true.

Changelog Entry

To be copied to the draft changelog by merger:

• CWL jobs with dynamic requirements now have input type checking properly protected by their conditionals.

Reviewer Checklist

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    contrib/admin/test-pr otheruser theirbranchname issues/XXXX-fix-the-thing
    

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Merger Checklist

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• Copy its recommended changelog entry to the Draft Changelog.
• Append the issue number in parentheses to the changelog entry.

[DailyDreaming]

LGTM.