Fix import script when generating rev-list to always return a list.

Note that in a situation where running the script with -generate_diffs
and only 1 migration script is running, the rev-list will return only a
single commit, which will be treated as a string instead of a list.
Therefore when indexing it with commits[0], in a case of a string, it
will return the first character instead of the first string as would be
expected.

import.ps1

@@ -123,7 +123,7 @@ function RunMigrationScriptsAndGenerateDiffs {
     git commit -m $tempUniqueCommitMessage
   }
   # Note that we're intentionally doing it this way, to be sure that we're not deleting commits we shouldn't
-  $commits = git rev-list --grep="$tempUniqueCommitMessage" --reverse HEAD
+  $commits = @(git rev-list --grep="$tempUniqueCommitMessage" --reverse HEAD)
   if ($commits.Count) {
     git reset --hard "$($commits[0])^1"
   }