Use debug snapshots for two redaction tests (#18077)
## Summary
Our redaction handling is already well covered here, but this switches
two tests to use snapshots to make them slightly clearer/more resilient
(e.g. in case we accidentally debug a token not as a string but as
bytes, in which case the previous naive string match would
false-negative here).
## Test Plan
But doctor, I am the unit tests.
Signed-off-by: William Woodruff <william@astral.sh>
