To allow testing against a Kerberos instance, we have added variables
for the Kerberos password to allow authentication against LIBGIT2.ORG in
commit e5fb5fe5 (ci: perform SPNEGO tests, 2019-10-20). To set up the
password, we assign

    "GITTEST_NEGOTIATE_PASSWORD=$(GITTEST_NEGOTIATE_PASSWORD)"

in the environmentVariables section which is then passed through to a
template. As the template does build-time expansion of the environment
variables, it will expand the above line verbosely, and due to the
envVar section not doing any further expansion the password variable
will end up with the value "$(GITTEST_NEGOTIATE_PASSWORD)" in the
container's environment.

Fix this fixed by doing expansion of GITTEST_NEGOTIATE_PASSWORD at
build-time, as well.