Fix typos found by codespell.

src/test/ui/issues/issue-31845.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Checks lexical scopes cannot see through normal module boundries
+// Checks lexical scopes cannot see through normal module boundaries
 
 fn f() {
     fn g() {}

src/test/ui/issues/issue-45696-no-variant-box-recur.rs

@@ -24,7 +24,7 @@
 
 // run-pass
 
-// This test has structs and functions that are by definiton unusable
+// This test has structs and functions that are by definition unusable
 // all over the place, so just go ahead and allow dead_code
 #![allow(dead_code)]
 

src/test/ui/issues/issue-50761.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Confirm that we don't accidently divide or mod by zero in llvm_type
+// Confirm that we don't accidentally divide or mod by zero in llvm_type
 
 // compile-pass