migrate dies when parsing files with duplicate timestamps

[nickpalmer]

Describe the Bug
When running migrations that were created with the same timestamp migrate will crash.

Steps to Reproduce
Steps to reproduce the behavior:

1. Write two migrations with the same timestamp

20220311025833_first.down.sql 
20220311025833_first.up.sql
20220311025833_second.down.sql
20220311025833_second.up.sql

2. Run migrate with these files

Expected Behavior
The migrations should run in alphabetical order without error

Migrate Version
dev

Loaded Source Drivers
file

Loaded Database Drivers
postgresql, stub, cockroach, cockroachdb, crdb-postgres, postgres

Go Version
go version go1.17.6 darwin/arm64

[DUWAPP01]

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