test(perf): increase cpu threshold (#6249)

## Problem
#6225
- Didn't think 400% could be exceeded, but this one is especially
volatile. Sometimes it barely spikes, and sometimes it goes crazy.
## Solution
- Increase to 500%

---

- Treat all work as PUBLIC. Private `feature/x` branches will not be
squash-merged at release time.
- Your code changes must meet the guidelines in
[CONTRIBUTING.md](https://github.com/aws/aws-toolkit-vscode/blob/master/CONTRIBUTING.md#guidelines).

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

packages/core/src/testInteg/perf/getFileSha384.test.ts

@@ -20,7 +20,7 @@ interface SetupResult {
 function performanceTestWrapper(label: string, fileSize: number) {
     return performanceTest(
         getEqualOSTestOptions({
-            userCpuUsage: 400,
+            userCpuUsage: 500,
             systemCpuUsage: 35,
             heapTotal: 4,
         }),