pin dask versions more strictly

4 jobs for dask in 10 minutes and 30 seconds (queued for 9 seconds)
Status Name Job ID Coverage
  Build
passed build_linux_38 #250881
bob docker

00:08:11

passed build_linux_39 #250882
bob docker

00:08:21

passed build_macos_intel_38 #250879
bob macos intel

00:10:26

passed build_macos_intel_39 #250880
bob macos intel

00:10:30