git: openjdk/skara: Use different scratch folders for different repos

[Robin Westberg]

Changeset: 9e9559ad
Author:    Robin Westberg <rwestberg at openjdk.org>
Date:      2020-02-11 14:30:20 +0000
URL:       https://git.openjdk.java.net/skara/commit/9e9559ad

Use different scratch folders for different repos

Reviewed-by: ehelin

! bots/pr/src/main/java/org/openjdk/skara/bots/pr/PullRequestInstance.java