release: Zephyr 1.9.0-rc4

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/Makefile b/Makefile
index 5bcdd84..c8c1a10 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@
 VERSION_MINOR 	   = 9
 PATCHLEVEL 	   = 0
 VERSION_RESERVED   = 0
-EXTRAVERSION       = -rc3
+EXTRAVERSION       = -rc4
 NAME 		   = Zephyr Kernel
 
 export SOURCE_DIR PROJECT