Remove semicolon from internal err macro

[Aaron1011]

This macro is used in expression position (a match arm), and only
compiles because of #33953

Regardless of what happens with that issue, this makes the
usage of the macro less confusing at the call site.

[rust-highfive]

r? @dtolnay

(rust_highfive has picked a reviewer for you, use r? to override)

[dtolnay]

Er, tidy fails.

Diff in /checkout/library/core/src/str/validations.rs at line 125:
         let old_offset = index;
         macro_rules! err {
             ($error_len: expr) => {
-                return Err(Utf8Error { valid_up_to: old_offset, error_len: $error_len })
+                return Err(Utf8Error { valid_up_to: old_offset, error_len: $error_len });
             };
         }

Running `"/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt" "--config-path" "/checkout" "--edition" "2018" "--unstable-features" "--skip-children" "--check" "/checkout/library/core/src/str/validations.rs"` failed.
If you're running `tidy`, try again with `--bless`. Or, if you just want to format code, run `./x.py fmt` instead.

[Aaron1011]

That's quite unfortunate - there might be a very large amount of code like #33953 in the wild due to rustfmt. I'll work on a rustfmt PR.

[Aaron1011]

@dtolnay: I've added a commit bumping the stage0 rustfmt to a version that accepts this code. This should now be ready to merge

[dtolnay]

@bors r+

[bors]

📌 Commit b03d4b0 has been approved by dtolnay

[bors]

⌛ Testing commit b03d4b0 with merge 7e20323...

[bors]

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing 7e20323 to master...