実際のところ
というわけで……(?)
passphrase-fileをつかって、
$ ssh robot@192.168.0.13 bash <<SHELL
> gpg --batch --passphrase-file password.txt --output example99.txt --decrypt testdata.txt.gpg
> SHELL
robot@192.168.0.13's password:
gpg: encrypted with 3072-bit RSA key, ID FB7BFEE9533DFC94, created 2019-08-17
"encrobot <encrobot@example.com>"