fix: make replacementName and Version not mergeable

[t-kulmburg]

Changes

Changes the config options replacementName and replacementVersion to be not mergeable.
Both are Strings that are used in package files exactly as they are written in the config, so merging them (in this case would mean appending two strings) does not make sense.

Context

This fixes this requested change in my other pull request, meaning i don`t need to make the change in the link at all.

Reason for this change is that I encountered a problem when working on replacements (#17882 & #17883):

Inside mergeChildConfig, when merging both replacementName and replacementVersion (both merging configs already had the same entries for both) the entry changed to an Array of single characters.

DEBUG: (repository=xx/renovate-test)
       "depName": {"0": "p", "1": "o", "2": "s", "3": "t", "4": "g", "5": "r", "6": "e", "7": "s"}
ERROR: Repository has unknown error (repository=xx/renovate-test)
       "err": {
         "message": "depName.replace is not a function",
         "stack": "TypeError: depName.replace is not a function\n    at sanitizeDepName ...
       }

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[renovate-release]

🎉 This PR is included in version 34.21.5 🎉

The release is available on:

• GitHub release
• 34.21.5

Your semantic-release bot 📦🚀