[FunctionNaming] Don't allow the usage of ` in function names

[BraisGabin]

From the Kotlin Coding conventions:

In tests (and only in tests), you can use method names with spaces enclosed in backticks.

https://kotlinlang.org/docs/coding-conventions.html#names-for-test-methods

And we are excluding this rule from test source sets so there is not point to alow it. It just allow false-negatives in production code.

[codecov]

Codecov Report

Merging #4439 (9eeff76) into main (eb0f1cf) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               main    #4439   +/-   ##
=========================================
  Coverage     84.32%   84.32%           
  Complexity     3293     3293           
=========================================
  Files           472      472           
  Lines         10522    10522           
  Branches       1885     1885           
=========================================
  Hits           8873     8873           
  Misses          671      671           
  Partials        978      978           

Impacted Files	Coverage Δ
...b/arturbosch/detekt/rules/naming/FunctionNaming.kt	100.00% <100.00%> (ø)

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