AMAZING SOLUTION --- No idea why, but it works if you follow this way:
I wanted to to some debuggings of this problem and Instead pushing the gexport-ed stuff directly to GitHub, I created a local bare git repo. Just to speed my debugging up ... but ... no error anymore, it worked directly.
I mirrored this bare afterwards to GitHub and updated hgrc to GitHub again ... still working.
This is my Step-by-step:
STEP B: Creating local bare
git init --bare account_invoice_line_standalone.git
STEP B: Editing .hg/hgrc
local = ../tryton_module_account_invoice_line_standalone.git
[git]
intree = 1
[extensions]
hgext.bookmarks =
git =
STEP C: Export hg to git objects
hg gexport
STEP D: Bookmark for master
hg bookmarks -r default master
STEP E: Pushing to local bare repository
hg push local
STEP F: Mirror bare repo to GitHub (it is never used atfer this procedure, you can delete the local bare)
git push --mirror git+ssh://g...@github.com/4commerce-technologies-AG/tryton_module_account_invoice_line_standalone.git
STEP G: Editing .hg/hgrc
STEP H: Pull hg updates and Export to git objects
hg pull
hg gexport
STEP I: Pushing Updates directly to GitHub repository (now it works ?!)
hg push github
Hope that someone here can fix this, that it is not neccessary to do the loop with local bare repo, but at least it works for us in the moment
Thanks for additional help
Tom