Ensure current image build value is taken into account when increment…

…ing build number

.github/scripts/update_image_descriptors.sh

@@ -17,6 +17,7 @@ function requiredEnv() {
 function nextImageVersion() {
     BUILD=1
     if [[ "${CURRENT_VERSION}" == ${ISPN_VERSION}* ]]; then
+        BUILD=${CURRENT_VERSION##*-}
         BUILD=$((BUILD+1))
     fi
     echo ${ISPN_VERSION}-${BUILD}