Add script and GH action to verify taps

[dsimansk]

Per title, adding a simple verification mechanism to check that taps work.

/cc @rhuss

Adding Productivity WG since it's Bash and actions, if you can take a look pls.
/cc @knative-extensions/productivity-writers

Fix #7

[knative-prow]

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In response to this:

Per title, adding a simple verification mechanism to check that taps work.

/cc @rhuss

Adding Productivity WG since it's Bash and actions, if you can take a look pls.
/cc @knative-extensions/productivity-writers

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[dsimansk]

I'll create very similar one for the main tap as well.

[dsimansk]

Required change to have test passing. Otherwise it's very nicely reporting failure. :)

[rhuss]

/lgtm
/approve

[dsimansk]

@rhuss fixed one more wrong checksum in [email protected]. All should be green now 🤞.

[rhuss]

/approve
/lgtm

[knative-prow]

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