Tweak/ftl build

[yubiuser]

What does this PR aim to accomplish?:

• Check inputs of composite actions for emptyness (see here and here).
• Trigger FTL builds on changes to workflow actions

This is a follow up on #72

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5. I have squashed any insignificant commits. (git rebase)
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[PromoFaux]

pre-test-passing approval.

[yubiuser]

🎉