Backward incompatilbe change in detect_ambiguities

[tkf]

I just noticed that #36962 removed imported keyword argument from Test.detect_ambiguities. Since it is not mentioned in the documentation (https://docs.julialang.org/en/v1.6-dev/stdlib/Test/), it is technically unclear if we need to treat detect_ambiguities as public API. However, as it is exported since 2016 (Julia v0.5) be8679e, I suggest to treat this function as a public API.

@vtjnash Is it possible to add the new algorithm without changing the signature? At least, I think it's better to keep imported and show depwarn when non-default value is given.

I can create a PR to add no-op imported keyword argument if that's an appropriate solution.

[vtjnash]

Yeah, it’d just be ignored now. I was assuming most users would need to delete Base from the module list to pass the test anyways, so hadn’t worried about it.