Update release_tools/version_tag.sh

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: kevinbackhouse

release_tools/version_tag.sh

@@ -12,7 +12,7 @@
 # that manually.
 
 # Check that the main branch is checked out.
-if [ $(git rev-parse --abbrev-ref HEAD) != "main" ] ; then
+if [ "$(git rev-parse --abbrev-ref HEAD)" != "main" ] ; then
     echo "Please check out the main branch before running this command."
     exit 1
 fi