Testing a new resource with basic auth gives errors

When I'm adding a new WMS resource, specify "Basic Authentication" username + password, and then press the "Test" button at the Action row at the bottom of the page, I'm getting a result indicating that the test has failed. Details:
```
{
"end_time": "2021-06-29T11:53:03Z",
"message": "(, XMLSyntaxError('xmlParseEntityRef: no name, line 18, column 48'), )",
"probes": [
{
"checks": [
{
"check_id": 9,
"class": "GeoHealthCheck.plugins.check.checks.HttpStatusNoError",
"message": "OK",
"name": "HTTP status should not be errored",
"response_time": -1,
"success": true
},
{
"check_id": 10,
"class": "GeoHealthCheck.plugins.check.checks.XmlParse",
"message": "(, XMLSyntaxError('xmlParseEntityRef: no name, line 18, column 48'), )",
"name": "Valid XML response",
"response_time": "0.167",
"success": false
},
{
"check_id": 11,
"class": "GeoHealthCheck.plugins.check.checks.NotContainsOwsException",
"message": "OK",
"name": "Response NOT contains OWS Exception",
"response_time": "0.14",
"success": true
},
{
"check_id": 12,
"class": "GeoHealthCheck.plugins.check.checks.ContainsStrings",
"message": "Title> not in response text",
"name": "Response contains strings",
"response_time": "0.13",
"success": false
}
],
"class": "GeoHealthCheck.plugins.probe.owsgetcaps.WmsGetCaps",
"message": "(, XMLSyntaxError('xmlParseEntityRef: no name, line 18, column 48'), )",
"name": "WMS GetCapabilities",
"probe_id": 3,
"response_time": "0.170545",
"success": false
}
],
"report_version": "1",
"resource_id": 2,
"resource_title": "Untitled",
"resource_type": "OGC:WMS",
"response_time": "0.177604",
"start_time": "2021-06-29T11:53:03Z",
"success": false,
"url": ""
}
```

I was expecting a successful test result. When I save and close the resource, reopen it and then press "Test now", then the test passes successfully. Also when I press "Edit" and then the same "Test" button as in the beginning, the test succeeds. It is as if the credentials aren't used when the new check isn't saved to the database yet.

Also note that the resource title is "Untitled", although I had already given the new resource a proper name before I performed the test.

Output of `docker logs ghc_web`:
```
2021-06-29 13:52:39,686 - urllib3.connectionpool - DEBUG - Starting new HTTPS connection (1): test.omgevingsserver.nl:443
2021-06-29 13:52:39,808 - urllib3.connectionpool - DEBUG - https://:443 "GET /bgt/ows?service=WMS&request=GetCapabilities&version=1.3.0 HTTP/1.1" 302 277
2021-06-29 13:52:39,845 - urllib3.connectionpool - DEBUG - https://:443 "GET /login.html?httpd_location=?service=WMS&request=GetCapabilities&version=1.3.0 HTTP/1.1" 200 1309
2021-06-29 13:52:39,847 - healthcheck - WARNING - Cannot use functools.partial(, version='1.3.0') on : xmlParseEntityRef: no name, line 18, column 48 (, line 18)
Traceback (most recent call last):
File "/GeoHealthCheck/GeoHealthCheck/healthcheck.py", line 175, in sniff_test_resource
ows = ows_handler(url)
File "/venv/lib/python3.7/site-packages/owslib/wms.py", line 56, in WebMapService
timeout=timeout, headers=headers, auth=auth)
File "/venv/lib/python3.7/site-packages/owslib/map/wms130.py", line 75, in __init__
self._capabilities = reader.read(self.url, timeout=self.timeout)
File "/venv/lib/python3.7/site-packages/owslib/map/common.py", line 69, in read
return etree.fromstring(raw_text)
File "src/lxml/etree.pyx", line 3237, in lxml.etree.fromstring
File "src/lxml/parser.pxi", line 1896, in lxml.etree._parseMemoryDocument
File "src/lxml/parser.pxi", line 1784, in lxml.etree._parseDoc
File "src/lxml/parser.pxi", line 1141, in lxml.etree._BaseParser._parseDoc
File "src/lxml/parser.pxi", line 615, in lxml.etree._ParserContext._handleParseResultDoc
File "src/lxml/parser.pxi", line 725, in lxml.etree._handleParseResult
File "src/lxml/parser.pxi", line 654, in lxml.etree._raiseParseError
File "", line 18
lxml.etree.XMLSyntaxError: xmlParseEntityRef: no name, line 18, column 48
2021-06-29 13:52:39,852 - urllib3.connectionpool - DEBUG - Starting new HTTPS connection (1): :443
2021-06-29 13:52:39,972 - urllib3.connectionpool - DEBUG - https://:443 "GET /bgt/ows?service=WMS&request=GetCapabilities&version=1.1.1 HTTP/1.1" 302 277
2021-06-29 13:52:40,016 - urllib3.connectionpool - DEBUG - https://:443 "GET /login.html?httpd_location=/bgt/ows?service=WMS&request=GetCapabilities&version=1.1.1 HTTP/1.1" 200 1309
2021-06-29 13:52:40,019 - healthcheck - WARNING - Cannot use functools.partial(, version='1.1.1') on : xmlParseEntityRef: no name, line 18, column 48 (, line 18)
Traceback (most recent call last):
File "/GeoHealthCheck/GeoHealthCheck/healthcheck.py", line 175, in sniff_test_resource
ows = ows_handler(url)
File "/venv/lib/python3.7/site-packages/owslib/wms.py", line 52, in WebMapService
timeout=timeout, headers=headers, auth=auth)
File "/venv/lib/python3.7/site-packages/owslib/map/wms111.py", line 75, in __init__
self._capabilities = reader.read(self.url, timeout=self.timeout)
File "/venv/lib/python3.7/site-packages/owslib/map/common.py", line 69, in read
return etree.fromstring(raw_text)
File "src/lxml/etree.pyx", line 3237, in lxml.etree.fromstring
File "src/lxml/parser.pxi", line 1896, in lxml.etree._parseMemoryDocument
File "src/lxml/parser.pxi", line 1784, in lxml.etree._parseDoc
File "src/lxml/parser.pxi", line 1141, in lxml.etree._BaseParser._parseDoc
File "src/lxml/parser.pxi", line 615, in lxml.etree._ParserContext._handleParseResultDoc
File "src/lxml/parser.pxi", line 725, in lxml.etree._handleParseResult
File "src/lxml/parser.pxi", line 654, in lxml.etree._raiseParseError
File "", line 18
lxml.etree.XMLSyntaxError: xmlParseEntityRef: no name, line 18, column 48
2021-06-29 13:52:40,020 - healthcheck - ERROR - Getting metadata failed: Cannot get OGC:WMS service instance for
Traceback (most recent call last):
File "/GeoHealthCheck/GeoHealthCheck/healthcheck.py", line 183, in sniff_test_resource
raise ValueError(message)
ValueError: Cannot get OGC:WMS service instance for
```

Note the line with `https://:443 "GET /login.html?httpd_location=?service=WMS&request=GetCapabilities&version=1.3.0 HTTP/1.1`. I've set up my web server in such a way that when no authorization headers are provided the user is redirected to a login page. Obviously this is not a valid GetCapabilities document, hence the various kinds of errors (invalid XML and missing Title string).