util/dofile.pl: require Text::Template 1.46 or newer

The reason is that we override Text::Template::append_text_to_output(),
and it didn't exist before Text::Template 1.46.

Fixes #6641

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6682)