Update sonic-py-swsssdk. (#7889)

Update sonic-py-swsssdk submodule to include below commits:
6be76f45 Add missing functions to be on par with swsscommon. (#107)
64232a0 (master) [CI] Setup proper Azp (#106)
9d019b0 [ci]: Set up CI with Azure Pipelines (#102)
fa760c4 Fix bug: use instance variable instead of class variable in ConfigDBConnector (#99)
Signed-off-by: Suvarna Meenakshi <sumeenak@microsoft.com>