bake: ensure remote files behind ssh expose agent

The updateContext function may make modifications to the build inputs,
creating either an SSH URL, or an SSH llb.State. In these cases, we need
to ensure that we appropriately expose the client's default agent.

Previously, we would only expose it if the remote context was a git URL,
however, we need to also ensure that if the input was used to override
the context (in the case of ReadRemoteFiles), that we expose the agent
here as well.

Signed-off-by: Justin Chadwell <me@jedevc.com>

bake/bake.go

@@ -1105,7 +1105,7 @@ func toBuildOpt(t *Target, inp *Input) (*build.Options, error) {
 	if err != nil {
 		return nil, err
 	}
-	if len(sshSpecs) == 0 && buildflags.IsGitSSH(contextPath) {
+	if len(sshSpecs) == 0 && (buildflags.IsGitSSH(bi.ContextPath) || (inp != nil && buildflags.IsGitSSH(inp.URL))) {
 		sshSpecs = append(sshSpecs, &controllerapi.SSH{ID: "default"})
 	}
 	sshAttachment, err := controllerapi.CreateSSH(sshSpecs)