We initially added `requireDocker` for a way for tasks to say that they
absolutely must have it, like the build docker image tasks.
Projects using the test fixtures plugin are not in this both, as the
intent with these is that they will be skipped if docker and docker-compose
is not available.
Before this change we were lenient, the docker image build would succeed
but produce nothing. The implementation was also confusing as it was not
immediately obvious this was the case due to all the indirection in the
code.
The reason we have this leniency is that when we added the docker image
build, docker was a fairly new requirement for us, and we didn't have
it deployed in CI widely enough nor had CI configured to prefer workers
with docker when possible. We are in a much better position now.
The other reason was other stack teams running `./gradlew assemble`
in their respective CI and the possibility of breaking them if docker is
not installed. We have been advocating for building specific distros for
some time now and I will also send out an additional notice
The PR also removes the use of `requireDocker` from tests that actually
use test fixtures and are ok without it, and fixes a bug in test
fixtures that would cause incorrect configuration and allow some tasks
to run when docker was not available and they shouldn't have.
Closes #42680 and #42829 see also #42719
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