attributeChangedCallback triggers a duplicate fetch of a board

[rdmurphy]

This is my bad — I forgot that attributeChangedCallback and connectedCallback will fire when a custom element connects.

I think the answer is to make sure the current value for this.href and the third parameter of attributeChangedCallback (often called newValue) do not match before allowing the fetch to happen.

[rdmurphy]

Instead going to borrow this incredibly basic approach from @github/remote-input-element and just validate whether oldValue exists or not!