File is too large to upload, while server limit is much higher

### Steps to reproduce

1. I set up a self-hosted Synapse server using the docker image: matrixdotorg/synapse:latest, 1dbbb05f33da
2. I raise the default `max_upload_size` config to 500M
3. I use a nginx reverse proxy, so I also set the `client_max_body_size 500M;`
```
location ~ ^(/_matrix|/_synapse/client) {
proxy_pass http://synapse;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Host $host;
# Nginx by default only allows file uploads up to 1M in size
# Increase client_max_body_size to match max_upload_size defined in homeserver.yaml
client_max_body_size 500M;
}
4. when I try to upload files (in element-android) that larger than 50M, it raise `File is too large to upload`
5. I try files with different sizes, 49M is ok, 53M is not ok.

```

### Outcome

#### What did you expect?
file <500M be uploaded
#### What happened instead?
file >50M failed to upload

### Your phone model

Google Pixel 4L

### Operating system version

Android 12

### Application version and app store

Element 1.3.15 from F-droid

### Homeserver

docker image: matrixdotorg/synapse:latest, hash:1dbbb05f33da

### Will you send logs?

No