release: Zephyr 2.7.0-rc4

Set version to 2.7.0-rc4

Signed-off-by: Christopher Friedt <chrisfriedt@gmail.com>
diff --git a/VERSION b/VERSION
index 0c383cd..119dca5 100644
--- a/VERSION
+++ b/VERSION
@@ -2,4 +2,4 @@
 VERSION_MINOR = 7
 PATCHLEVEL = 0
 VERSION_TWEAK = 0
-EXTRAVERSION = rc3
+EXTRAVERSION = rc4