add jdk 16 and 17 to ci

[XenoAmess]

Hey,

Thanks for the contribution, this is awesome.
As you may have read, project members have somehow an opinionated view on what and how should be
Mockito, e.g. we don't want mockito to be a feature bloat.
There may be a thorough review, with feedback -> code change loop.

Which branch :

• On mockito 3.x, make your pull request target release/3.x
• On mockito 2.x, make your pull request target release/2.x (2.x is in maintenance mode)

This block can be removed
_Something wrong in the template fix it here .github/PULL_REQUEST_TEMPLATE.md

check list

• Read the contributing guide
• PR should be motivated, i.e. what does it fix, why, and if relevant how
• If possible / relevant include an example in the description, that could help all readers
  including project members to get a better picture of the change
• Avoid other runtime dependencies
• Meaningful commit history ; intention is important please rebase your commit history so that each
  commit is meaningful and help the people that will explore a change in 2 years
• The pull request follows coding style
• Mention Fixes #<issue number> in the description if relevant
• At least one commit should mention Fixes #<issue number> if relevant

[TimvdLippe]

Gradle does not support JDK 16+ yet, so we are blocked on gradle/gradle#13481 for now.

[XenoAmess]

Gradle does not support JDK 16+ yet, so we are blocked on gradle/gradle#13481 for now.

@TimvdLippe
Yes indeed. This pr is just for showing this using ci (for tracking a jdk 16 bug in another repo who use mockito). we can close it.