Change contextConflictMessage to reflect the fact that is being thrown when SmartContract method is being called without 'await'

[dfstio]

The following error is being thrown when calling SmartContract method without await:

Error: It seems you're running multiple provers concurrently within the same JavaScript thread, which, at the moment, is not supported and would lead to bugs.

Proposal: change the wording to reflect the fact that this error may mean that await should be used to call SmartContract methods

https://github.com/o1-labs/o1js/blob/main/src/lib/util/global-context.ts#L106