release/deploy-github: add rudimentary checks for tag existence

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

release/deploy-github.sh

@@ -4,6 +4,14 @@ trap 'exit 1' SIGINT SIGTERM
 
 [ -z "$(command -v hub)" ] && { echo "hub not installed; aborting!"; exit 1; }
 [ -z "${1}" ] && { echo "No tag specified!"; exit 1; }
+found_tag=
+git tag -l | while read -r tag; do
+  if [ "$tag" == "${1}" ]; then
+    found_tag=true
+    break
+  fi
+done
+[ -z "${found_tag}" ] && { echo "Cannot find tag ${1} in the repository"; exit 1; }
 prev_ref="$(git rev-parse --abbrev-ref HEAD)"
 git checkout "${1}"
 gradle clean bundleRelease assembleRelease