Rollup merge of #122328 - Enselic:sig_dfl-not-inherit, r=davidtwco

unix_sigpipe: Replace `inherit` with `sig_dfl` in syntax tests

The `sig_dfl` variant of the attribute is the most likely variant to be stabilized first, and thus to become the "most allowed" variant of the attribute. Because of this, it is the most appropriate variant to use in syntax tests, because even if the most allowed variant is used, the compiler shall still emit errors if it e.g. is used in the wrong places.

r? ``@davidtwco`` who already [approved ](rust-lang/rust#120832 (review)) this commit in rust-lang/rust#120832.

It would be nice to land the last preparatory commit of that PR before we begin to [rename ](rust-lang/rust#120832 (comment)) things which will of course create a lot of code conflicts.

Author: workingjubilee