Add 'helm' ecosystem to dependabot-2.0 schema (SchemaStore#4679)

Dependabot recently added support for Helm charts, with the identifier
"helm". For details, see:

https://docs.github.com/en/code-security/dependabot/ecosystems-supported-by-dependabot/supported-ecosystems-and-repositories#supported-ecosystems-and-repositories

Author: evan-cz

src/schemas/json/dependabot-2.0.json

@@ -660,6 +660,7 @@
         "github-actions",
         "gomod",
         "gradle",
+        "helm",
         "maven",
         "mix",
         "npm",