fix(test): fix failing integ tests. (aws#5724)

## Problem
In the recent refactor
(aws#5689), there is a
mismatch in args between our fs and fs-extra. Not caught until integ
tests were run.

## Solution
have default write file method ignores encoding since it uses utf8
anyway.

---

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License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

Author: Hweinstock

packages/core/src/stepFunctions/utils.ts

@@ -69,8 +69,8 @@ export class StateMachineGraphCache {
             })
         this.writeFile =
             writeFileCustom ??
-            (async (path: string, data: string, encoding: string) => {
-                await fs.writeFile(path, data, { mode: encoding })
+            (async (path: string, data: string, _encoding: string) => {
+                await fs.writeFile(path, data)
             })
         this.logger = getLogger()
         this.getFileData = getFileData ?? httpsGetRequestWrapper