fix(ci): helm unittest is broken (#787)

see comments

### Test plan

CI pass now

(cherry picked from commit b9369b8)

Author: michaellzc

scripts/ci/helm-unittest.sh

@@ -2,8 +2,12 @@
 
 set -euf -o pipefail
 
+# 1.0.3 is broken now
+# https://github.com/helm-unittest/helm-unittest/issues/790
+HELM_UNITTEST_VERSION="v1.0.2"
+
 ### Install the helm-unittest plugin
-helm plugin install https://github.com/helm-unittest/helm-unittest
+helm plugin install https://github.com/helm-unittest/helm-unittest --version "$HELM_UNITTEST_VERSION"
 
 ### Run the helm tests
 helm unittest -q charts/sourcegraph