Add test case for issue #64732

Author: onehr

src/test/ui/issues/issue-64732.rs

@@ -0,0 +1,9 @@
+#![allow(unused)]
+fn main() {
+    let _foo = b'hello\0';
+    //~^ ERROR character literal may only contain one codepoint
+    //~| HELP if you meant to write a byte string literal, use double quotes
+    let _bar = 'hello';
+    //~^ ERROR character literal may only contain one codepoint
+    //~| HELP if you meant to write a `str` literal, use double quotes
+}

src/test/ui/issues/issue-64732.stderr

@@ -0,0 +1,22 @@
+error: character literal may only contain one codepoint
+  --> $DIR/issue-64732.rs:3:17
+   |
+LL |     let _foo = b'hello\0';
+   |                 ^^^^^^^^^
+help: if you meant to write a byte string literal, use double quotes
+   |
+LL |     let _foo = b"hello\0";
+   |                 ^^^^^^^^^
+
+error: character literal may only contain one codepoint
+  --> $DIR/issue-64732.rs:6:16
+   |
+LL |     let _bar = 'hello';
+   |                ^^^^^^^
+help: if you meant to write a `str` literal, use double quotes
+   |
+LL |     let _bar = "hello";
+   |                ^^^^^^^
+
+error: aborting due to 2 previous errors
+