Address flaky unit tests

[jviau]

Using this issue to track flaky unit tests as they are discovered.

Flaky tests

Fix PR	Test	Failed Run
#10128	azure-functions-host/test/WebJobs.Script.Tests/FileMonitoringServiceTests.cs Line 286 in 1bf0813 public static async Task TestAppOfflineDebounceTime(string fileName, int delayInMs, bool expectShutdown, bool expectRestart)	N/A
TBD	azure-functions-host/test/WebJobs.Script.Tests/Security/SecretManagerTests.cs Line 938 in 1bf0813 public async Task AddOrUpdateFunctionSecret_ClearsCache_WhenHostLevelFunctionSecretAdded()	Failed run
#10145	azure-functions-host/test/WebJobs.Script.Tests/Workers/Http/HttpFunctionInvocationDispatcherTests.cs Line 23 in 1bf0813 public async Task TestDelay_StartProcess(bool startWorkerProcessResult)	Failed run
#10146	azure-functions-host/test/WebJobs.Script.Tests/FunctionsSyncServiceTests.cs Line 18 in 1bf0813 public class FunctionsSyncServiceTests
TBD	https://github.com/Azure/azure-functions-host/blob/1bf081347aa0ff3fa02e846802ae330611d192ff/test/WebJobs.Script.Tests.Integration/WebHostEndToEnd/WebJobsStartupEndToEndTests.cs
TBD	azure-functions-host/test/WebJobs.Script.Tests/StartupContextProviderTests.cs Line 77 in d223fa7 public async Task GetHostSecretsOrNull_ReturnsExpectedSecrets()	Failed run

Tasks

Beta Give feedback

1. Fix flaky test TestDelay_StartProcess by restructuring task model #10145
   +0
2. Address flaky TestAppOfflineDebounceTime test #10128
   +0
3. Flaky test: FunctionsSyncServiceTests: Increase test due time & add tsc callback #10146
   +0
4. [in-proc backport] Flaky test: FunctionsSyncServiceTests: Increase test due time & add tsc callback #10146 #10152
   +0
5. [in-proc backport] Fix flaky test by restructuring task model (#10145) #10172
   +0