The flag -s will instruct keepassxc-cli to use the same password for
both databases. You will have to enter the password, though. You can
of course automate this even further by having a file that provides
the password to your database. Straddeling convenience and security is
left as an exercise to the reader. ;)
"keepassxc-cli merge" is not a silver bullet. It can lose data. Make sure to check the output to spot any merges that might have gone haywire.
Naturally this would also be the place to advice to "always backup your database before performing merges" – but hey, your database is already stored in a git repo.
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