[MC-261264] The advancement "Two by Two" is no longer obtainable due to the change to sniffer's breeding

Breeding sniffers now drops a sniffer egg instead of spawning a snifflet, but the advancement "Two by Two" still requires the snifflet's immediate spawning, causing it unobtainable.

In husbandry/bred_all_animals.json, the criterion is as follows:

...
    "minecraft:sniffer": {
      "conditions": {
        "child": [
          {
            "condition": "minecraft:entity_properties",
            "entity": "this",
            "predicate": {
              "type": "minecraft:sniffer"
            }
          }
        ]
      },
      "trigger": "minecraft:bred_animals"
    }, 
...

This should be fixed as:

...
    "minecraft:sniffer": {
      "conditions": {
        "parent": [
          {
            "condition": "minecraft:entity_properties",
            "entity": "this",
            "predicate": {
              "type": "minecraft:sniffer"
            }
          }
        ],
        "partner": [
          {
            "condition": "minecraft:entity_properties",
            "entity": "this",
            "predicate": {
              "type": "minecraft:sniffer"
            }
          }
        ]
      },
      "trigger": "minecraft:bred_animals"
    },
...