Replace one item element slice for sequences like str with first slice index

[Gobot1234]

Checklist

• [x] I think this refactoring is useful for everyone (if it's too specific, consider a custom rule)
• [x] I have checked there are no similar issues suggesting the same thing

Description

For "hello world"[4:5] this can be safely replaced with "hello world"[4] and I think the intent is much clearer. There might be other sequences this can be applied to but I'm not currently aware of any.

Code Before

"hello world"[4:5]

Code After

"hello world"[4]

[Hellebore]

Thanks - I've added this to our backlog.