Fix typo in VariableUnusedViaUnset test

Tests/VariableUnusedViaUnset/CMakeLists.txt

@@ -1,7 +1,7 @@
 # NOTE: Changing lines in here changes the test results since the first
 # instance shouldn't warn, but the second should and they have the same message
 
-# A warning should NOT ne issued for this line:
+# A warning should NOT be issued for this line:
 set(UNUSED_VARIABLE)
 # Warning should occur here:
 set(UNUSED_VARIABLE)