Test #conficting_dependencies with a locking parent dependabot fixture

[Nishnha]

This PR adds a new test for UpdateChecker#conflicting_dependencies which uses a locking parent fixture so that the vulnerable transtitive dependency can't be upgraded.

I created and published npm-parent-dependency-5 which has only 1 version v1.0.0 and requires exactly npm-intermediate-dependency@0.0.1. In turn, this version of npm-intermediate-dependency requires exactly npm-transitive-dependency@v1.0.0, locking it from upgrading to the non vulnerable v1.0.1.

This test is subltly different from the "with a conflicting dependency and an unsatisfiable vulnerablity" test that already exists because it uses a valid vulnerable version range for npm-transitive-dependency of < 1.0.0 which could be satisfied by upgrading to v1.0.1. Meanwhile, the existing test uses a version range that cannot be satisfied, < 1.0.2, because no such version of npm-transitive-dependency exists.