test(conformance): g4 sees a doubling appended to what the field held

Redaction cost the gate this shape on android: the driver typed the value twice
onto existing content, so the whole value is not its own doubling and the typed
value is not in the trace to compare against. The recorded-value check still
catches it on the backends that record one.

Red at this commit: G4 reports PASS on a field that grew by one string twice.

conformance/testdata/g4-appended-doubling/output.log

@@ -0,0 +1 @@
+run complete