CompatHelper: bump compat for MCMCChains to 5 for package test, (keep existing compat) (#321)

This pull request changes the compat entry for the `MCMCChains` package from `4.0.4` to `4.0.4, 5` for package test.
This keeps the compat entries for earlier versions.



Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

Author: github-actions[bot]

test/Project.toml

@@ -26,7 +26,7 @@ Distributions = "0.25"
 DistributionsAD = "0.6.3"
 Documenter = "0.26.1, 0.27"
 ForwardDiff = "0.10.12"
-MCMCChains = "4.0.4"
+MCMCChains = "4.0.4, 5"
 MacroTools = "0.5.5"
 StableRNGs = "1"
 Tracker = "0.2.11"