Thanks for your answer.
The only solution other than turning SSL verification off was to set http.sslCAInfo to the 'pem' file created by gitBlit as
discussed here.
However if you do that then any other access to Github or Gitlab will fail, because it's now apparently only looking at this one specific file. There is a more specific configuration that uses part of the url of the repository and then only applies the self signed cert to that specifically. See the link above.
Setting the http.sslCert control as outlined the the gitblit documentation did not work, neither did setting http.sslCAPath.
This is all very confusing. I had expected that I could just install a certificate on the machine similar to how its done for a browser.
gary