Assign PR touching triagebot.toml to Philipp (#14590)

`triagebot.toml` is related to the repo behavior wrt interactions, and
must be kept inline with what is done in the CI.

changelog: none

r? @flip1995

Author: flip1995

triagebot.toml

@@ -44,6 +44,7 @@ users_on_vacation = [
 
 [assign.owners]
 "/.github" = ["@flip1995"]
+"/triagebot.toml" = ["@flip1995"]
 "/book" = ["@flip1995"]
 "*" = [
     "@Manishearth",