Fix mismatched quotation mark

tests/ui/mir/mir-inlining/always-encode-mirs.rs

@@ -1,6 +1,6 @@
 // Regression test for MIR inlining with -Zalways-encode-mir enabled in the auxiliary crate.
 // Previously we inlined function not eligible for inlining which lead to linking error:
-// undefined reference to `internal::S'
+// undefined reference to `internal::S`
 //
 //@ aux-build:internal.rs
 //@ build-pass