fix(graphql): findLinkedNodeByField not returning any value (#11045)

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## Description
`findLinkedNodeByField` does not return anything. This PR adds the missing `return`.
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## Related Issues

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  Link to the issue that is fixed by this PR (if there is one)
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Author: DanielRuf

packages/gatsby/src/schema/infer-graphql-type.js

@@ -189,7 +189,7 @@ function inferFromMapping(
 }
 
 function findLinkedNodeByField(linkedField, value) {
-  getNodes().find(n => n[linkedField] === value)
+  return getNodes().find(n => n[linkedField] === value)
 }
 
 export function findLinkedNode(value, linkedField, path) {