Fix UseCompatibleSyntax class error message

[rjmholt]

PR Summary

A bug in the UseCompatibleSyntax rule means error messages come out looking very bad. This fixes that.

PR Checklist

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• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
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[bergmeister]

Good spot. Looks good to me.
Optional suggestion would be to create a wrapper function for creating the error message since there are now 6 usages of Strings.UseCompatibleSyntaxError, this would improve readability when using named parameters to call it and would also add a small safety net since one only sees a mismatch of number of parameter at runtime.

[JamesWTruher]

looks fine