Fix ICE due to carriage return w/ multibyte char

Based off of
kfitch@972560b

src/librustc_parse_format/lib.rs

@@ -760,7 +760,7 @@ fn find_skips_from_snippet(
                 (' ' | '\n' | '\t', _) if eat_ws => {
                     skips.push(pos);
                 }
-                ('\\', Some((next_pos, 'n' | 't' | '0' | '\\' | '\'' | '\"'))) => {
+                ('\\', Some((next_pos, 'n' | 't' | 'r' | '0' | '\\' | '\'' | '\"'))) => {
                     skips.push(*next_pos);
                     let _ = s.next();
                 }

src/test/ui/issues/issue-70381.rs

@@ -0,0 +1,6 @@
+// Test that multi-byte unicode characters with missing parameters do not ICE.
+
+fn main() {
+  println!("\r¡{}")
+  //~^ ERROR 1 positional argument in format string
+}

src/test/ui/issues/issue-70381.stderr

@@ -0,0 +1,8 @@
+error: 1 positional argument in format string, but no arguments were given
+  --> $DIR/issue-70381.rs:4:16
+   |
+LL |   println!("\r¡{}")
+   |                ^^
+
+error: aborting due to previous error
+