dirmngr: Add CSRF protection exception for protonmail.

* dirmngr/http.c (same_host_p): Add exception table.

Please: Adding entries to this table shall be an exception and not the
rule.

(cherry picked from commit 134c3c16523b1a267ebdd2df6339240fd9e1e3b3)

• Signed-off-by: Werner Koch <wk@gnupg.org>