Non-working web app using up-to-date Azure quickstart guide

> Please provide us with the following information:
> ---------------------------------------------------------------

### This issue is for a: (mark with an `x`)
```
- [x] bug report -> please search issues before submitting
- [ ] feature request
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

### Minimal steps to reproduce
> 1. Follow the official steps on [Microsoft's website](https://learn.microsoft.com/en-us/azure/app-service/quickstart-python?tabs=flask%2Cmac-linux%2Cazure-portal%2Clocal-git-deploy%2Cdeploy-instructions-azportal%2Cterminal-bash%2Cdeploy-instructions-zip-azcli) to deploy the example Python3.9-based web app.

### Any log messages given by the failure
> Local build and deployment works, however, the site is not accessible. The reason is a Flask dependency issue as [documented here](https://stackoverflow.com/questions/77213053/why-did-flask-start-failing-with-importerror-cannot-import-name-url-quote-fr).

### Expected/desired behavior
> Web app accessible.

### OS and Version?
> Linux deployment on Azure app services

### Versions
> Python3.9

### Mention any other details that might be useful

There are already multiple PRs attempting to fix this issue:
- https://github.com/Azure-Samples/msdocs-python-flask-webapp-quickstart/pull/33
- https://github.com/Azure-Samples/msdocs-python-flask-webapp-quickstart/pull/32
- https://github.com/Azure-Samples/msdocs-python-flask-webapp-quickstart/pull/24

> ---------------------------------------------------------------
> Thanks! We'll be in touch soon.

Start by reviewing the Azure quickstart deployment steps and the existing PRs #33, #32, and #24, then examine the reported Flask dependency failure on Linux Azure App Service with Python 3.9. Done means the sample deploys successfully and the web app is accessible.

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