Update version in main/php_version.h as well

Otherwise the file is modified by each new build, what is confusing.

Author: cmb69

main/php_version.h

@@ -2,7 +2,7 @@
 /* edit configure.ac to change version number */
 #define PHP_MAJOR_VERSION 7
 #define PHP_MINOR_VERSION 4
-#define PHP_RELEASE_VERSION 17
+#define PHP_RELEASE_VERSION 18
 #define PHP_EXTRA_VERSION "-dev"
-#define PHP_VERSION "7.4.17-dev"
-#define PHP_VERSION_ID 70417
+#define PHP_VERSION "7.4.18-dev"
+#define PHP_VERSION_ID 70418