Add trybuild test to ensure deprecated types are derivable.

[daniel-levin]

Addresses #553.

#553 talks about warnings, but trybuild tests operate on compile errors. I think this change still manages to meet the spirit of #553. The docstring at the top of absence_of_deprecated_warning.rs explains the test. In short, there is "only" one compile error in the test.

If you comment out the #[allow(deprecated)] attribute in zerocopy-derive/src/lib.rs, then this test will fail.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.71%. Comparing base (7b77668) to head (5c31d15).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1332   +/-   ##
=======================================
  Coverage   87.71%   87.71%           
=======================================
  Files          15       15           
  Lines        5138     5138           
=======================================
  Hits         4507     4507           
  Misses        631      631           

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[jswrenn]

Thank you for this! Just a minor nit.

[jswrenn]

Thanks for the PR!

[daniel-levin]

I needed to update the line numbers in the trybuild test because the licence header changed them. I squashed the modifications and force pushed.