[Integrated] RFR: Use headHash instead of targetRef when fetching PRs

[Erik Helin]

Changeset: c63ac247
Author:    Erik Helin <ehelin at openjdk.org>
Date:      2019-12-03 09:02:33 +0000
URL:       https://git.openjdk.java.net/skara/commit/c63ac247

Use headHash instead of targetRef when fetching PRs

Reviewed-by: rwestberg

! bots/tester/src/main/java/org/openjdk/skara/bots/tester/TestWorkItem.java
! bots/tester/src/test/java/org/openjdk/skara/bots/tester/InMemoryPullRequest.java
! bots/tester/src/test/java/org/openjdk/skara/bots/tester/TestWorkItemTests.java