log/slog: add test case for level_test.go
adds a test case for the MarshalJSON and MarshalText method of the Level type in the slog package.
Change-Id: I3f79f0b46c41252ad9d743e03e34503e19998f3e
GitHub-Last-Rev:
dab00d4c206ca59fcca7ee8d97ca8cdc9475fdce
GitHub-Pull-Request: golang/go#65525
Reviewed-on: https://go-review.googlesource.com/c/go/+/561315
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>