fix(enterprise/coderd): identify audit rows by content instead of order in diff tests - #27904

…er in diff tests

GetAuditLogsOffset orders by time only, and audit timestamps are rounded
to microsecond. On Windows CI the clock resolution is coarse enough that
the create and update audit rows frequently tie, making the returned
order nondeterministic and flaking TestUserSecretAuditDiffRedaction.

Select rows by audit action (or by diff content where both rows share an
action) instead of by slice position in the four audit diff tests that
relied on ordering.

Fixes coder/internal#1625