Don't format tests/run-make/*/rmake.rs.

It's reasonable to want to, but in the current implementation this
causes multiple problems.

- All the `rmake.rs` files are formatted every time even when they
  haven't changed. This is because they get whitelisted unconditionally
  in the `OverrideBuilder`, before the changed files get added.

- The way `OverrideBuilder` works, if any files gets whitelisted then no
  unmentioned files will get traversed. This is surprising, and means
  that the `rmake.rs` entries broke the use of explicit paths to `x
  fmt`, and also broke `GITHUB_ACTIONS=true git check --fmt`.

The commit removes the `rmake.rs` entries, fixes the formatting of a
couple of files that were misformatted (not previously caught due to the
`GITHUB_ACTIONS` breakage), and bans `!`-prefixed entries in
`rustfmt.toml` because they cause all these problems.

compiler/rustc_mir_transform/src/validate.rs

@@ -691,7 +691,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                                 location,
                                 format!(
                                     "You can't project to field {f:?} of `DynMetadata` because \
-                                         layout is weird and thinks it doesn't have fields."
+                                     layout is weird and thinks it doesn't have fields."
                                 ),
                             );
                         }