`unnecessary_debug_formatting` should respect MSRV

[dswij]

Summary

unnecessary_debug_formatting doesn't have MSRV config and currently lints for lower than minimum MSRV.

See also #14955 (comment)

[donkomura]

@rustbot claim

[Jarcho]

The referenced comment is incorrect. Path::display doesn't need an msrv.

[lopopolo]

OsStr::display does have an MSRV

[Jarcho]

Your linked commit is adding an allow on Path::display not OsStr::display. The impl for Slice<OsStr> is the impl above that.