Test placeholder based on complete image.

[jrouly]

Took me a long time to figure out what was going on here.

I have custom cloner and placeholder images. They are hosted on a private registry in the same image repository and differentiated by tags. For example,

example.com/drone:git
example.com/drone:placeholder

These images are multiplatform images based on drone/git and drone/placeholder.

Because these images differ only in tag, the check image.Match (which explicitly ignores tags) is detecting the cloner step as having completed with the placeholder image -- i.e., the placeholder failed(!). This is detected as a step/framework error and the stage aborts.

I really have no idea why we would want to exclude tag here.

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