Existing client re-use without credentials set

I found another unexpected behavior:

If I read a property with a specific `formIndex`
```
const interactionOutput = await thing.readProperty("test", { formIndex: 0 });
```
and if a client already exists I get a client for that protocol without `credentials` set. If no client exists everything works fine.

https://github.com/eclipse/thingweb.node-wot/blob/07494392e1def691f06adeae4224afac7cd4cd65/packages/core/src/consumed-thing.ts#L491
This retrieves the client from servient leading to a client without `credentials`.

https://github.com/eclipse/thingweb.node-wot/blob/07494392e1def691f06adeae4224afac7cd4cd65/packages/core/src/consumed-thing.ts#L493
This instead returns a valid client with `credentials` set.

Should the client always be retrieved with `this.getClients().get(scheme)` like here?
https://github.com/eclipse/thingweb.node-wot/blob/07494392e1def691f06adeae4224afac7cd4cd65/packages/core/src/consumed-thing.ts#L512

_Originally posted by @ilovemilk in https://github.com/eclipse/thingweb.node-wot/issues/890#issuecomment-1339239278_