scrabble: false positive 'LoopRuneNotByte' suggestion

[Solution 59997d1a390d44568ad4664a7ea13d9e](https://exercism.io/mentor/solutions/59997d1a390d44568ad4664a7ea13d9e) produces this suggestion:

> Iterating over a string produces runes. A rune represents a Unicode character and can consist of multiple bytes. Try using runes instead of bytes.

But the solution does use runes:

```go
// Package scrabble provides functions to play the game scrabble.
package scrabble

import "strings"

// Score takes a string and returns its scrabble score as an integer.
func Score(word string) int {
scores := map[string]int{
"aeioulnrst": 1,
"dg": 2,
"bcmp": 3,
"fhvwy": 4,
"k": 5,
"jx": 8,
"qz": 10,
}

var ret int

word = strings.ToLower(word)

for _, j := range word {
for k := range scores {
if strings.ContainsRune(k, j) {
ret += scores[k]
}
}
}

return ret
}
```

Reproduce the LoopRuneNotByte suggestion using the linked Scrabble solution and the code shown in the issue. Trace the analyzer rule that emits this message; done means rune iteration using strings.ContainsRune is not reported while genuine byte/rune mistakes still are, with a regression test covering this case.

Written by the indexing model from the issue text.