[sonic-swss-common] Submodule Update (#6812)

Change in this update:
    b75aab7 [swss-common] Add LINKMGR CFG and MUX LINKMGR state table names (#421)
    4a77d1c [ci]: add vstest (#459)
    07258a6 [ci]: use build template (#457)
    ddcae3e runRedisScript api to process integer returned by script run in the redis (#447)
    33d89c7 [systemlag] Schema defs for system lag (#448)
    af01f37 spell check fixes (#456)
    7afd43d Update to make getNamespaces() API at par with the get_ns_list() swssdk-py API. (#455)

signed-off-by: Tamer Ahmed <tamer.ahmed@microsoft.com>