Update version to 1.67.4-dev (#7940)

diff --git a/version.go b/version.go
index 35728c2..580b5d2 100644
--- a/version.go
+++ b/version.go
@@ -19,4 +19,4 @@
 package grpc
 
 // Version is the current grpc version.
-const Version = "1.67.3"
+const Version = "1.67.4-dev"