fix: stringify response headers as ALB expects response headers to be type string

This was identified through using express within AWS Lambda which returns content-length header as a number which causes ALB to throw a 502 bad gateway exception. This change fixes this issue.

Author: Jack-Overflow

src/event-sources/aws/alb.js

@@ -52,7 +52,7 @@ const getResponseToAlb = ({
   const multiValueHeaders = !event.headers ? getMultiValueHeaders({ headers: responseHeaders }) : undefined
   const headers = event.headers
     ? Object.entries(responseHeaders).reduce((acc, [k, v]) => {
-      acc[k] = Array.isArray(v) ? v[0] : v
+      acc[k] = Array.isArray(v) ? String(v[0]) : String(v)
       return acc
     }, {})
     : undefined