[guides] Use `match ..., via: :all` in the custom exceptions app [ci skip]

Using `get` results in an unexpected error page(returning empty body) for requests of other HTTP mehtods other than GET. Use `match ..., via:
:all` so the exceptions app can be more stable.
Merge pull request #16832 from yuki24/use-match-via-all-in-custom-exceptions-app

[guides] Use `match ..., via: :all` in the custom exceptions app [ci skip]