Unify usage of GHA workflows from rusefi/rusefi repository

[kifir23917]

Currently Create Board Firmware GHA workflow reuses workflow from ext/rusefi submodule, while Update rusEFI Reference GHA workflow reuses workflow directly from rusefi/rusefi repository.
This potentially can cause inconsistency in versions of GHA workflows in use (for example we can unintentially use workflows from different branches).
Do we need to consider unification for ways of reusing GHA workflows from rusefi/rusefi repository?

[rusefillc]

Definitely but zero priority until we figure out which approach is better when and why.

[chuckwagoncomputing]

Create Board Firmware uses the custom action from the submodule because of this:
rusefi/rusefi#6114

The value of unification seems small to me.
Using a workflow/custom action from the submodule comes with downsides, listed in rusefi/rusefi#6162