ci: fix the publication process of a version already released

.github/scripts/check_version.sh

@@ -7,16 +7,16 @@ version=`grep "^version" gradle.properties | cut -d= -f2 | tr -d "[:space:]"`
 echo "Version in 'gradle.properties' file: '$version'"
 
 if [ "$tag" != "" ]; then
+  echo "Release mode: check version consistency..."
   if [ "$tag" != "$version" ]; then
     echo "ERROR: the tag '$tag' is different from the version '$version' in the 'gradle.properties' file"
     exit 1
   fi
-fi
-
-echo "Fetch tags..."
-git fetch --tags
-
-if [ $(git tag -l "$version") ]; then
-  echo "ERROR: version '$version' has already been released"
-  exit 1
+else
+  echo "Snapshot mode: fetch existing tags..."
+  git fetch --tags
+  if [ $(git tag -l "$version") ]; then
+    echo "ERROR: version '$version' has already been released"
+    exit 1
+  fi
 fi