Use IdentitiesOnly=yes option in QA git clone

What does this MR do and why?

Without the SSH option -o IdentitiesOnly=yes the SSH client will attempt to authenticate with every public key that it has. This can cause failures in tests if there are enough identities to cause the SSH client to give up before it tries the key specified via the command-line.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.