Time-stamp-compatibility on emacs 31.0.50

[eval-exec]

Hello, Thanks for your great project. When I launch rust-playground from emacs 31.0.50, it popup a buffer:

The formats recognized in time-stamp-format will change in a future release
to be more compatible with the format-time-string function.

The following obsolescent time-stamp-format construct(s) were found:

"%:y" -- use %Y
"%:y" -- use %Y

It seems that rust-playground should replace %:y by %Y.