test weird $dynamicRef/$dynamicAnchor bookending case

[ryangalamb]

This case comes from a slack conversation with @jdesrosiers .

[ssilverman]

👍

[jdesrosiers]

This looks to me like it's testing the normal case of looking for the bookend in the initially resolved schema, which is covered in #462. The weird case (to me at least) is when a $dynamicRef ends up behaving like a $ref if it isn't used properly.

{
    "$dynamicAnchor": "foo",
    "type": "object",
    "properties": {
        "foo": { "$dynamicRef": "dynamic.json#foo" },
        "bar": { "$dynamicRef": "not-dynamic.json#foo" },
        "baz": { "$dynamicRef": "wtf.json" },
    },
    "$defs": {
        "dynamic": {
            "$id": "dynamic.json",
            "$dynamicAnchor": "foo",
            "not": true
        },
        "not-dynamic": {
            "$id": "not-dynamic.json",
            "$anchor": "foo",
            "not": true
        },
        "wtf": {
            "$id": "wtf.json",
            "not": true
        }
    }
}

• /foo is weird because it references a schema that will never be used for anything other than checking if it has a dynamic anchor.
• /bar is weird because it's a dynamic reference to a non-dynamic anchor, which is only valid because it reverts to behaving like $ref if used improperly. (This is covered in Add tests for $dynamicRef/$dynamicAnchor #462)
• /baz is the weirdest because it doesn't even reference an anchor. It's not even pretending to be dynamic. Again, it's only valid because it reverts to behaving like $ref if used improperly. (@amosonn brought up this case in Add tests for refs with relative uris #457, but decided to make a separate issue to cover this case.)

[Julian]

@jdesrosiers I take the above as you suggesting to close this PR (with thanks to you @rjmill) but let me know if I misunderstood.