encoding/json/v2: fix wrong type with cyclic marshal error in map[string]any
The type reported in a ErrCycle is the wrong type due to a typo.
This discrepency was detected by setting optimizeCommon to false
and running the tests.
This only modifies code that is compiled in under goexperiment.jsonv2.
Change-Id: I68268f5c719d8b79a67424a35ed0647adf12288c
Reviewed-on: https://go-review.googlesource.com/c/go/+/695277 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Damien Neil <dneil@google.com>