ci: unify bash calling convention

Under ci/ hierarchy, we run scripts under either "sh" (any Bourne compatible POSIX shell would work) or specifically "bash" (as they require features from bash, e.g., ${parameter/pattern/string} expansion). As we have the CI environment under our control, we can expect that /bin/sh will always be fine to run the scripts that only require a Bourne shell, but we may not know where "bash" is installed depending on the distro used. So let's make sure we start these scripts with either one of these: #!/bin/sh #!/usr/bin/env bash Yes, the latter has to assume that everybody installs "env" at that path and not as /bin/env or /usr/local/bin/env, but this currently is the best we could do. Signed-off-by: Junio C Hamano <gitster@pobox.com>