Misconfigured `sendVariableValues` results in similar behavior as `{all: true}`
### Issue Description

When configuring `ApolloServerPluginUsageReporting`, if you misconfigure `sendVariableValues` it seems to result in the same behavior as `{all: true}`.

#### Intended outcome
I think I would expect either an error due to the misconfiguration or a better logical fallback inline with `{none: true}`.


#### Actual outcome
We mistakenly set `sendVariableValues` to a function instead of `transform` and then saw all variables sent to apollo studio.

```js
      sendVariableValues: ({ operationString, variables }) => {
        if (includes(operationString, "search")) {
          return { searchTerm: variables?.searchTerm };
        }

        // Return an empty object or null for other queries to avoid logging any data
        return {};
      }
```

I can fork and add this to git if you'd like
```js
  it('Random config does not filter variables', () => {
    // @ts-ignore
    expect(makeTraceDetails(variables, { literally: 'anything but a good value' })).toEqual(
      nonFilteredOutput,
    );
  });
```

### Link to Reproduction

https://codesandbox.io/p/devbox/stupefied-faraday-4vfmt4

### Reproduction Steps

_No response_