Make the GC scripts executables

gc.sh and utils.sh are shell scripts that should be
executable in order to be used E2E.

Change-Id: Ib1cc77a089ebff95726b20eb5311855a99fc7a09
diff --git a/maintenance/git-gc/scripts/gc.sh b/maintenance/git-gc/scripts/gc.sh
old mode 100644
new mode 100755
diff --git a/maintenance/git-gc/scripts/utils.sh b/maintenance/git-gc/scripts/utils.sh
old mode 100644
new mode 100755