replaced deprecated jenkins.getInstance() calls with .get() (#5269)

* replaced deprecated jenkins.getInstance() calls with .get()

* Apply suggestions from code review

Co-authored-by: Oleg Nenashev <o.v.nenashev@gmail.com>

* Apply suggestions from code review

Co-authored-by: Daniel Beck <1831569+daniel-beck@users.noreply.github.com>

Co-authored-by: Oleg Nenashev <o.v.nenashev@gmail.com>
Co-authored-by: Daniel Beck <1831569+daniel-beck@users.noreply.github.com>