gnucash-docs: New annotated tag '5.1'

[John Ralls]

        at  https://github.com/Gnucash/gnucash-docs/tree/f0cd9ec229976a3b5d14c19f6b229bf5965738c5 (tag)
   tagging  ca2ed412c9fe64bf5b2ecb646edfb102f784334e (commit)
  replaces  5.0
 tagged by  John Ralls
        on  Sat Apr 29 15:34:34 2023 -0700


Release Documentation for GnuCash 5.1

Geert Janssens (1):
      Add details to a few csv import line options

John Ralls (2):
      Remove Ubuntu-18.04 jobs from CI.
      Release Documentation for GnuCash 5.1