requests.exceptions.HTTPError: 404 Client Error: Not Found for url

[sofisl]

When using synthtool to generate a new library for templates (or, for any case where the call doesn't match the repo), this error occurs:

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/local/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/synthtool/synthtool/languages/node.py", line 358, in <module>
    owlbot_main()
  File "/synthtool/synthtool/languages/node.py", line 349, in owlbot_main
    templates = common_templates.node_library(
  File "/synthtool/synthtool/gcp/common.py", line 301, in node_library
    return self._generic_library("node_library", **kwargs)
  File "/synthtool/synthtool/gcp/common.py", line 64, in _generic_library
    kwargs["metadata"]["repo"]["default_branch"] = _get_default_branch_name(
  File "/synthtool/synthtool/gcp/common.py", line 374, in _get_default_branch_name
    github_req.raise_for_status()
  File "/usr/local/lib/python3.9/site-packages/requests/models.py", line 943, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: Not Found for url: https://api.github.com/repos/googleapis/nodejs-essential-contacts

This error makes sense because the repository hasn't been published, but we still need to continue this call as we need to generate the base templates.

This issue can be traced to this fix.