Advisories deleted from source Git repository not being marked as withdrawn

[andrewpollock]

Describe the bug
Whilst doing some validation analysis for bitnami/vulndb#336 I noticed that records now showing as deleted are not marked as withdrawn in OSV.dev

Then I remembered #829 removed this behaviour due to some sort of blip at the time in the GitHub Advisory Database, whereas a safer approach would be to do a threshold-based operation like what's being done for GCS in #2030

Expected behaviour
I was of the expectation that deleted records were marked as withdrawn and that Git-based source imports would catch up to the commits deleting a record

Additional context

• Don't mark deleted git entries as invalid. #829

• https://osv.dev/vulnerability/BIT-typo3-2023-47127

• https://github.com/bitnami/vulndb/tree/main/data/typo3/BIT-typo3-2023-47127.json

• bitnami/vulndb@54689e9