cli: allow --bank to be mutable in submit/bulksubmit

Problem: The `-B, --bank=` option does not appear in the set of
mutable options/args in submit/bulksubmit.

Add it to mutable_args.

Author: grondo

src/bindings/python/flux/cli/base.py

@@ -505,6 +505,7 @@ class Xcmd:
     #  the string representation of an Xcmd object.
     mutable_args = {
         "queue": "-q",
+        "bank": "-B",
         "ntasks": "-n",
         "nodes": "-N",
         "cores_per_task": "-c",