BugBug landings risk report: JSONDecodeError: Expecting value: line 1 column 1 (char 0)

https://community-tc.services.mozilla.com/tasks/IVZ14W11TRuWUNcKm_g59A/runs/0/logs/public/logs/live.log#L1689:

2025-12-22 00:35:41,632:INFO:scripts.generate_landings_risk_report:Download previous test info...
2025-12-22 00:35:42,316:INFO:bugbug.db:Downloading https://community-tc.services.mozilla.com/api/index/v1/task/project.bugbug.landings_risk_report.latest/artifacts/public/test_info.json.zst to data/test_info.json.zst
a/test_info.json.zst : 0 B...     
                                                                               
data/test_info.json.zst: 1645405 bytes 
2025-12-22 00:35:43,097:INFO:scripts.generate_landings_risk_report:Get previously gathered test info...
  0% 0/90 [00:00<?, ?it/s]
 98% 88/90 [00:01<00:00, 60.15it/s]
100% 90/90 [00:02<00:00, 30.11it/s]
                                                                               
Read:     0   B /  1.56 MiB ==>  0%
                                                                               
data/test_info.json  :  8.67%   (  1.56 MiB =>    138 KiB, data/test_info.json.zst) 
Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/requests/models.py", line 976, in json
    return complexjson.loads(self.text, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/json/__init__.py", line 346, in loads
    return _default_decoder.decode(s)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/usr/local/bin/bugbug-generate-landings-risk-report", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/usr/local/lib/python3.12/site-packages/scripts/generate_landings_risk_report.py", line 1894, in main
    landings_risk_report_generator.go(args.days)
  File "/usr/local/lib/python3.12/site-packages/scripts/generate_landings_risk_report.py", line 854, in go
    "nightly": get_crash_signatures("nightly"),
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/scripts/generate_landings_risk_report.py", line 122, in get_crash_signatures
    response = r.json()
               ^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/requests/models.py", line 980, in json
    raise RequestsJSONDecodeError(e.msg, e.doc, e.pos)
requests.exceptions.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Start with scripts/generate_landings_risk_report.py and get_crash_signatures at line 122, then reproduce the landings risk report run while inspecting the response passed to r.json(). Done means the report completes without this JSON decoding failure and handles the observed response appropriately.