devel/php-composer: Update to 2.6.4

The main composer port contains old and long EOLed/deprecated version
1.x of the software.

Move the devel/php-composer2 port over, dropping it, and update to
latest version.

Please check UPDATING entry 20230930, to correctly update use
"pkg install phpXX-composer" (replacing XX with the PHP shorthand
version you're using)

PR: 274160
Approved by: Naram Qashat <cyberbotx@cyberbotx.com> (maintainer)
Security: 33922b84-5f09-11ee-b63d-0897988a1c07