fix: fix slice init length

[cuishuang]

The intention here should be to initialize a slice with a capacity of len(g.ChildGroups) rather than initializing the length of this slice.

The online demo: https://go.dev/play/p/q1BcVCmvidW

[antoninbas]

Thank for for this fix!
@tnqn @Dyanngg do you think this is something worth backporting? I can see how this bug would not really impact functionality, but it would create some incorrect index entries, with the "" key matching all groups (but we probably never lookup that key).

[Dyanngg]

Thank for for this fix! @tnqn @Dyanngg do you think this is something worth backporting? I can see how this bug would not really impact functionality, but it would create some incorrect index entries, with the "" key matching all groups (but we probably never lookup that key).

Yes can confirm that we never use "" to look up this index

[antoninbas]

/test-all