Add D7 variables for CORE_LEG_PHP, _TARGET_D7_PHP and _TARGET_D7_DB_VERSION

Migrated issue

Reported by: fjgarlin

Related to !271 (merged)

Problem/Motivation

#3463894: Update templates so 11.0 is the default/current branch Step 3 and final was happening today, but we want to do a last minute check with Drupal 7 pipelines and PHPUnit jobs to make sure that the changes made to key variables on the templates don't have a negative effect on the Drupal 7 jobs.

Steps to reproduce

Test the "main" (latest) changes on some Drupal 7 projects.

Proposed resolution

Not sure if anything will need changing.

Remaining tasks

MR?

Related issue: Issue #3463894