[chore] bump to 3.0.3-rc03 (#44521)

Author: gavinchou

gensrc/script/gen_build_version.sh

@@ -31,7 +31,7 @@ build_version_prefix="doris"
 build_version_major=3
 build_version_minor=0
 build_version_patch=3
-build_version_rc_version="rc02"
+build_version_rc_version="rc03"
 
 build_version="${build_version_prefix}-${build_version_major}.${build_version_minor}.${build_version_patch}-${build_version_rc_version}"