git-mwcore macro used wrong reference

The git-mwcore macro 203c8f2c https://gerrit.wikimedia.org/r/#/c/84949/
was not using the proper reference repository, having
/srv/ssd/zuul/git/mediawiki/core instead of the Gerrit replicated bare
repository.

Jobs updated:

mediawiki-core-doxygen-publish
mediawiki-core-install-sqlite
mediawiki-core-jsduck
mediawiki-core-jsduck-publish
mediawiki-core-lint
mediawiki-core-phpunit-api
mediawiki-core-phpunit-databaseless
mediawiki-core-phpunit-misc
mediawiki-core-phpunit-parser
mediawiki-core-qunit
mediawiki-core-regression-REL1_19
mediawiki-core-regression-REL1_20
mediawiki-core-regression-REL1_21
mediawiki-core-regression-REL1_22
mediawiki-core-regression-master
mediawiki-core-whitespaces

Change-Id: I59223a2d13978b23317109fda0e3b0d23e977acd