Fix url escaping on exceptions dashboard for non-string keys

[phofl]

Closes #xxxx

• Tests added / passed
• Passes pre-commit run --all-files

[phofl]

Here is a reproducer that raised previously:

if __name__ == "__main__":
    cluster = LocalCluster()
    client = cluster.get_client()
    print(cluster.dashboard_link)

    def test(i):
        raise NotImplementedError

    res = client.submit(test, 10, key=1)

    time.sleep(100)