fix: avoid panic when parsing the create index on timestamp with/without time zone

[bbckr]

When running the latest version of goerd against a schema that has a WHERE clause specifying timestamp with/without timezone, it would panic.

panic: runtime error: slice bounds out of range [62:1]

goroutine 1 [running]:
github.com/covrom/goerd/drivers/postgres/idxscan.ParseCreateIndex({0x14000216540?, 0x1400003d878?})
        /Users/user/go/pkg/mod/github.com/covrom/goerd@v1.1.1/drivers/postgres/idxscan/idxscan.go:53 +0x448
github.com/covrom/goerd/drivers/postgres.(*Postgres).Analyze(0x1400003db58, 0x14000146a00)
        /Users/user/go/pkg/mod/github.com/covrom/goerd@v1.1.1/drivers/postgres/postgres.go:253 +0x22f0
github.com/covrom/goerd/datasource.Analyze({0x16d3769c4, 0x84})
        /Users/user/go/pkg/mod/github.com/covrom/goerd@v1.1.1/datasource/datasource.go:24 +0x1d4
github.com/covrom/goerd.SchemaFromPostgresWithConnect(...)
        /Users/user/go/pkg/mod/github.com/covrom/goerd@v1.1.1/goerd.go:14
main.main()
        /Users/user/go/pkg/mod/github.com/covrom/goerd@v1.1.1/cmd/goerd/main.go:185 +0xd34

This is because with utail we index on WITH, and that ends up matching the WITH or WITHOUT in the WHERE clause.

Can be reproduced and validated with the newly added unit tests.

[bbckr]

Hey @covrom, mind taking a look at this?