This is a small "duplicated error message" bug fix which is not directly related to  the issue 10326.

With `pragma(msg, is(int == invariant));`:

Before:
```
test.d(1): Deprecation: use of 'invariant' rather than 'immutable' is deprecated
test.d(1): Deprecation: use of 'invariant' rather than 'immutable' is deprecated
```

After:
```
test.d(1): Error: use 'immutable' instead of 'invariant'
```