RFR: checkout: fetch origin before checking out branch

[Erik Helin]

Hi all,

please review this small patch that ensures that we fetches the remote `origin` before checking the source branch in the `checkout` bot. This is to ensure that the we have a local ref to the source branch in case we are are operating on a local Git repository that hasn't been updated in a while.

Thanks,
Erik

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Commit messages:
 - checkout: fetch origin before checking out branch

Changes: https://git.openjdk.java.net/skara/pull/999/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=999&range=00
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/999.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/999/head:pull/999

PR: https://git.openjdk.java.net/skara/pull/999