fix building from git url without a protocol

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

client/llb/source.go

@@ -254,6 +254,9 @@ func Git(remote, ref string, opts ...GitOption) State {
 			remote = parts[0] + "/" + parts[1]
 		}
 	}
+	if protocolType == gitProtocolUnknown {
+		url = "https://" + url
+	}
 
 	id := remote
 

source/identifier.go

@@ -102,6 +102,9 @@ func FromLLB(op *pb.Op_Source, platform *pb.Platform) (Identifier, error) {
 					id.KeepGitDir = true
 				}
 			case pb.AttrFullRemoteURL:
+				if !isGitTransport(v) {
+					v = "https://" + v
+				}
 				id.Remote = v
 			case pb.AttrAuthHeaderSecret:
 				id.AuthHeaderSecret = v