Add PR number to test README

Author: xylar

components/mpas-ocean/cime_config/testdefs/testmods_dirs/mpaso/scaled_dib_dismf/README

@@ -1,5 +1,5 @@
 This testdef is used to test a stealth feature in mpaso and mpassi introduced
-by PR #XXXX. It simply changes sets the following namelist option in mpaso
+by PR #6696. It simply changes sets the following namelist option in mpaso
 to true
    config_scale_dismf_by_removed_ice_runoff
 and the following namelist option in mpassi to true