all: Bump version to 1.28.0.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

py/mpconfig.h

@@ -41,7 +41,7 @@
 #define MICROPY_VERSION_MAJOR 1
 #define MICROPY_VERSION_MINOR 28
 #define MICROPY_VERSION_MICRO 0
-#define MICROPY_VERSION_PRERELEASE 1
+#define MICROPY_VERSION_PRERELEASE 0
 
 // Combined version as a 32-bit number for convenience to allow version
 // comparison. Doesn't include prerelease state.