Fix `TestThumbnailsStorage` failing when media results come back in non-deterministic order; silence expected error when tests are run multiple times against the same postgres database (cherry-picked from #2395)
Fix `TestThumbnailsStorage` failing when media results come back in non-deterministic order; silence expected
error when tests are run multiple times against the same postgres database (cherry-picked from #2395)

Signed-off-by: Brian Meek <760e7dab2836853c63805033e514668301fa9c47@hntlabs.com>

matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite