Upgrade govuk_dependabot_merger config to use v2 #498

Job	Run time
test_matrix (3.1)	23s
test_matrix (3.2)	17s
test_matrix (3.3)	20s
Dependency Review scan / dependency-review-pr	0s
Dependency Review scan / dependency-review-push	2m 5s
CodeQL SAST scan / Analyze	1m 14s
SNYK security analysis / sast	31s
SNYK security analysis / sca	0s
test	1s
generate_pacts	23s
asset_manager_pact / Verify pact tests	45s
account_api_pact / Verify pact tests	48s
collections_pact / Verify pact tests	14s
imminence_pact / Verify pact tests	57s
email_alert_api_pact / Verify pact tests	1m 11s
frontend_pact / Verify pact tests	13s
link_checker_api_pact / Verify pact tests	38s
locations_api_pact / Verify pact tests	47s
publishing_api_pact / Verify pact tests	49s
publish_pacts	0s
publish_gem	0s
	11m 36s

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