devel/php-xdebug: update to 3.0.0

pkgsrc change: use standard PECL site as MASTER_SITES.

Mon, Feb 22, 2021 - Xdebug 3.0.3

Fixed bugs:

- Fixed issue #1930: No local variables with trigger and xdebug_break()
- Fixed issue #1931: xdebug_info() output misses configuration
  settings if phpinfo() has been called
- Fixed issue #1932: One line in multi-line string concatenation is
  not covered
- Fixed issue #1940: Wrong type used for showing GC Stats reports

(taca)