Allow typings for InngestFunction["client"] (#803)

## Summary
<!-- Succinctly describe your change, providing context, what you've
changed, and why. -->

Allows typings to be published for `myFn["client"]`.

## Checklist
<!-- Tick these items off as you progress. -->
<!-- If an item isn't applicable, ideally please strikeout the item by
wrapping it in "~~"" and suffix it with "N/A My reason for skipping
this." -->
<!-- e.g. "- [ ] ~~Added tests~~ N/A Only touches docs" -->

- [ ] ~Added a [docs PR](https://github.com/inngest/website) that
references this PR~ N/A Abstract change
- [ ] ~Added unit/integration tests~ N/A
- [x] Added changesets if applicable

.changeset/dirty-poets-begin.md

@@ -0,0 +1,5 @@
+---
+"inngest": patch
+---
+
+`myFn["client"]` is now typed

packages/inngest/src/components/InngestFunction.ts

@@ -53,7 +53,7 @@ export class InngestFunction<
   public readonly opts: TFnOpts;
   private readonly fn: THandler;
   private readonly onFailureFn?: TFailureHandler;
-  private readonly client: TClient;
+  protected readonly client: TClient;
   private readonly middleware: Promise<MiddlewareRegisterReturn[]>;
 
   /**