Please, CI needs to run all plugins tests OR remind to add testsuite when new plugin is added

[Anton-Latukha]

In #2530 lead to: #2530 (comment)

On adding a new plugin - people on both sides of the review can forget (& CI would give a wrong impression that everything passes) that CI does not have plugin check. So CI actually does not check that the plugin works properly & contributor & reviewer can merge it.

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1. CI conf can be done in a way that it automatically runs/generates test suite runs forall plugins.
2. When the new directory into plugins is added, or when the list of dirs there do not match the literal list - remind to add the test suite hook into `test.

[Anton-Latukha]

The easiest way every Haskeller would think looking into test.yml & would think to fmap over the list of plugins. In idiomatic GitHub (& in most of other CIs) terms that would be to matrix on plugins.

But there are ~15-20 plugins. GitHub invalidates/terminates CI workflow if matrix expands >256 instances (even if we deforest most of them right in the code - GitHub does not count deforestation).

So the solution should be default

[Anton-Latukha]

DHall would also allow solving this in the Haskell way.