Form Recognizer API with Python for PDF throwing "BadArgument" error

> The issue
> ---------------------------------------------------------------

The Quickstart for Form Recognizer REST API with Python is not functioning any more. It throws the following error:
`
POST analyze failed:
{"error":{"code":"BadArgument","message":"Bad or unrecognizable request JSON or binary file."}}
`

Not sure if this has to do with the update to Form Recognizer REST API v3.0, but is not functioning for PDF anymore. It worked a few weeks ago.

### My code

```
from requests import get, post, Request, Session

endpoint = r"https://westeurope.api.cognitive.microsoft.com"
key = ""

def get_url(filename, endpoint, apim_key):

# v2.1
post_url = endpoint + "/formrecognizer/v2.1/layout/analyze"

headers = {
# Request headers
'Content-Type': 'application/pdf',
'Ocp-Apim-Subscription-Key': apim_key,
}

with open(filename, "rb") as f:
data_bytes = f.read()

try:
resp = post(post_url, data=data_bytes, headers=headers)
if resp.status_code != 202:
print("POST analyze failed:\n%s" % resp.text)
return None
print("POST analyze succeeded: %s" % resp.headers["operation-location"])
get_url = resp.headers["operation-location"]
return get_url
except Exception as e:
print("POST request failed:\n%s" % str(e))
return None

resp_url = get_url(source, endpoint, key)
```

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

### Minimal steps to reproduce
> Follow the Quickstart: Extract text and layout information using the Form Recognizer REST API with Python

### Any log messages given by the failure
> POST analyze failed:
{"error":{"code":"BadArgument","message":"Bad or unrecognizable request JSON or binary file."}}

### Expected/desired behavior
> I would expect to get a url returned

### OS and Version?
> Working on Windows 10, using Visual Studio Code

### Versions
> requests == 2.28.1
> Python == 3.9.13

Start by following the “Extract text and layout information using the Form Recognizer REST API with Python” Quickstart and compare its request with the failing get_url function and the reported Form Recognizer v2.1 endpoint. Reproduce the BadArgument response using the supplied PDF request, then verify that the corrected Quickstart returns an operation URL without the error.

Written by the indexing model from the issue text.