Explanation of the error
Salesforce surfaces the validation error of "Cannot specify: inlineHelpText for platform event field" when your Platform Event metadata has a field which has the inlineHelpText attribute specified.
Resolution
This is due to be fixed by Salesforce in the Summer ‘23 release, however as a workaround for now remove the inlineHelpText from your Platform Event metadata type.
Further examples of this Salesforce validation error can be found here:
Disclaimer: This error is returned by Salesforce directly, rather than Gearset. Even so, we offer guidance based on our combined experience with the Metadata API. Where possible, we try to help guide you to fix or avoid this error. In the case that this isn't possible, we may need to direct you to Salesforce support for further clarification.