tests: fix telemetry span timeout (#5473)

Problem:
- "returns the correct call stack when the context switches" uses sleep under the hood which requires manual ticks when fake clocks are installed. When we added the fake clock it caused this test to fail

Solution:
- only install the fake clock for "records performance"

Author: jpinkney-aws

packages/core/src/test/shared/telemetry/spans.test.ts

@@ -96,18 +96,17 @@ describe('TelemetrySpan', function () {
 
 describe('TelemetryTracer', function () {
     let tracer: TelemetryTracer
-    let clock: ReturnType<typeof installFakeClock>
+    let clock: ReturnType<typeof installFakeClock> | undefined
     let sandbox: SinonSandbox
     const metricName = 'test_metric' as MetricName
 
     beforeEach(function () {
         tracer = new TelemetryTracer()
-        clock = installFakeClock()
         sandbox = sinon.createSandbox()
     })
 
     afterEach(function () {
-        clock.uninstall()
+        clock?.uninstall()
         sandbox.restore()
     })
 
@@ -269,11 +268,12 @@ describe('TelemetryTracer', function () {
         })
 
         it('records performance', function () {
+            clock = installFakeClock()
             const { expectedCpuUsage, expectedHeapTotal } = stubPerformance(sandbox)
             tracer.run(
                 'function_call',
                 () => {
-                    clock.tick(90)
+                    clock?.tick(90)
                 },
                 {
                     trackPerformance: true,