Merge pull request nestjs#3589 from tonyhallett/createguardsfunction-return-type-correction

refactor(core): change return type annotation to be exact

Author: kamilmysliwiec

packages/core/router/router-execution-context.ts

@@ -325,7 +325,7 @@ export class RouterExecutionContext {
     instance: Controller,
     callback: (...args: any[]) => any,
     contextType?: TContext,
-  ): Function | null {
+  ): (args: any[]) => Promise<void> | null {
     const canActivateFn = async (args: any[]) => {
       const canActivate = await this.guardsConsumer.tryActivate<TContext>(
         guards,