**List of steps to reproduce** (step by step, including full links if applicable):
* Attempt to copy-upload a file from the Internet Archive using Pywikibot:
```
site.upload(filepage, source_url=file_url,
comment=desc)
```
**What happens?**:
* If the upload succeeds, the call still hangs:
```
File "./script.py", line 105, in upload
self.site.upload(filepage, source_url=file_url,
File "/usr/lib/python3.9/site-packages/pywikibot/tools/_deprecate.py", line 404, in wrapper
return obj(*__args, **__kw)
File "/usr/lib/python3.9/site-packages/pywikibot/site/_decorators.py", line 92, in callee
return fn(self, *args, **kwargs)
File "/usr/lib/python3.9/site-packages/pywikibot/site/_apisite.py", line 2869, in upload
result = final_request.submit()
File "/usr/lib/python3.9/site-packages/pywikibot/data/api.py", line 1757, in submit
response, use_get = self._http_request(use_get, uri, body, headers,
File "/usr/lib/python3.9/site-packages/pywikibot/data/api.py", line 1510, in _http_request
self.wait()
File "/usr/lib/python3.9/site-packages/pywikibot/data/api.py", line 1892, in wait
pywikibot.sleep(delay)
File "/usr/lib/python3.9/site-packages/pywikibot/__init__.py", line 1305, in sleep
```
It looks like the handler is catching the 504 which is often returned, and retrying forever. However, during a copy upload, a 504 is very common, but the file may still upload.
**What should have happened instead?**:
* Call either succeeds, or times out and allows the script to continue.
**Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc**: