fix inheritance of sidekiq securityContext

[roobre]

values.yaml says:

  sidekiq:
    # -- Pod security context for all Sidekiq Pods, overwrites .Values.podSecurityContext
    podSecurityContext: {}
    # -- (Sidekiq Container) Security Context for all Pods, overwrites .Values.securityContext
    securityContext: {}

However, this was not true before this PR: Only sidekiq.securityContext was considered, defaulting to an empty security context if it was not set.

[timetinytim]

Ah good catch, thank you!