Fix Logger process-level calls on older Elixir

Elixir 1.11-1.13 expose Logger.put_process_level/1 and
Logger.delete_process_level/0, while newer versions use process-aware
arities. Add a compatibility helper in ConfigTest that dispatches by
function_exported?/3 and uses apply/3 to avoid compile-time
undefined-function warnings, which restores OTP 24 CI runs.

Author: tombruijn

test/appsignal/config_test.exs

@@ -1490,8 +1490,20 @@ defmodule Appsignal.ConfigTest do
   end
 
   defp without_logger(fun) do
-    Logger.put_process_level(self(), :none)
+    put_process_level(self(), :none)
     fun.()
-    Logger.delete_process_level(self())
+    delete_process_level(self())
+  end
+
+  # Logger process-level APIs differ between Elixir versions:
+  # older versions expose arities without pid, newer versions include pid.
+  # Use dynamic dispatch so OTP 24 CI (Elixir 1.11-1.13) and newer
+  # versions both compile and run these tests.
+  if function_exported?(Logger, :put_process_level, 2) do
+    defp put_process_level(pid, level), do: apply(Logger, :put_process_level, [pid, level])
+    defp delete_process_level(pid), do: apply(Logger, :delete_process_level, [pid])
+  else
+    defp put_process_level(_pid, level), do: apply(Logger, :put_process_level, [level])
+    defp delete_process_level(_pid), do: apply(Logger, :delete_process_level, [])
   end
 end