Updating galaxy requirements doesn't work

Summary

Updating tags in galaxy fails.

Steps to reproduce

Try to update galaxy requirements

Expected behavior

Tags gets updated

Actual behavior

Error in console, nothing is changed

Relevant logs and/or screenshots

fatal: [localhost]: FAILED! => {"failed": true, "msg": "the field 'args' has an invalid value, which appears to include a variable that is undefined. The error was: '_updater_modified_file_lines' is undefined\n\nThe error appears to have been in '/home/pstemplewski/repos/apl/auto-updater/roles/updater/tasks/merge_request/create_change_galaxy.yml': line 2, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n---\n- name: \"change a tag in galaxy file\"\n  ^ here\n"}

Possible fixes

In this MR variable changes from _updater_modified_file_lines: [] to _updater_modified_file: ''.

So we can declare another variable with old name (then updating galaxy should work) or change code in create_change_galaxy.yml to use new variable