tests: add regression test for rust-lang#74745

This commit adds a regression test for rust-lang#74745. While a
`ignore-tidy-trailing-lines` header is required, this doesn't stop the
test from reproducing, so long as there is no newline at the end of the
file.

However, adding the header comments made the test fail due to a bug in
pprust, fixed in the previous commit.

Signed-off-by: David Wood <david@davidtw.co>

Author: davidtwco

src/test/pretty/issue-74745.rs

@@ -0,0 +1,5 @@
+// ignore-tidy-trailing-newlines
+// pretty-compare-only
+
+/*
+*/