Flip AVIF_VERSION_DEVEL back to 1 for v1.2.1 (#2694)

include/avif/avif.h

diff --git a/include/avif/avif.h b/include/avif/avif.h
index c05b4c8..62199cd 100644
--- a/include/avif/avif.h
+++ b/include/avif/avif.h
@@ -80,7 +80,7 @@
 #define AVIF_VERSION_MAJOR 1
 #define AVIF_VERSION_MINOR 2
 #define AVIF_VERSION_PATCH 1
-#define AVIF_VERSION_DEVEL 0
+#define AVIF_VERSION_DEVEL 1
 #define AVIF_VERSION \
     ((AVIF_VERSION_MAJOR * 1000000) + (AVIF_VERSION_MINOR * 10000) + (AVIF_VERSION_PATCH * 100) + AVIF_VERSION_DEVEL)