Fixes for GitHub API access

[chrisbillowsMO]

Fixes/improvements for the use of the GitHub API for fetching commit information for the HTML report, (ref: #4036/#4075)

1. Revise how the token passed into the environment
2. When a token is missing, the try/except does not catch the HTTP error (e.g. see below). If there is a problem with the token/API etc then the report should still generate, just without the commit information.

Traceback (most recent call last):
  File "/home/b/b382148/cylc-run/recipe_test_workflow_production/run2/app/generate_report/bin/fetch_commit_info.py", 
line 96, in make_api_call
    raise requests.exceptions.HTTPError(
    ...<2 lines>...
    )
requests.exceptions.HTTPError: Unexpected status code for url=https://api.github.com/repos/ESMValGroup/ESMValCore/com
mits/71604c36 headers={'authorization': 'token None', 'accept': 'application/vnd.github+json'} params=None - 401: {"m
essage":"Bad credentials","documentation_url":"https://docs.github.com/rest","status":"401"}

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/b/b382148/cylc-run/recipe_test_workflow_production/run2/app/generate_report/bin/generate_html_report.py
", line 491, in <module>
    main()
    ~~~~^^
  File "/home/b/b382148/cylc-run/recipe_test_workflow_production/run2/app/generate_report/bin/generate_html_report.py
", line 132, in main
    commit_info = fetch_commit_details_from_github_api(sha_info)
  File "/home/b/b382148/cylc-run/recipe_test_workflow_production/run2/app/generate_report/bin/fetch_commit_info.py", 
line 46, in fetch_commit_details_from_github_api
    raw_commits = fetch_single_commit(
        package, "ESMValGroup", headers, shas_by_day["today"]
    )
  File "/home/b/b382148/cylc-run/recipe_test_workflow_production/run2/app/generate_report/bin/fetch_commit_info.py", 
line 141, in fetch_single_commit
    response = make_api_call(url, headers=headers)
  File "/home/b/b382148/cylc-run/recipe_test_workflow_production/run2/app/generate_report/bin/fetch_commit_info.py", 
line 101, in make_api_call
    raise requests.exceptions.HTTPError(
        f"HTTP error occurred: {http_err}"
    ) from http_err
requests.exceptions.HTTPError: HTTP error occurred: Unexpected status code for url=https://api.github.com/repos/ESMVa
lGroup/ESMValCore/commits/71604c36 headers={'authorization': 'token None', 'accept': 'application/vnd.github+json'} p
arams=None - 401: {"message":"Bad credentials","documentation_url":"https://docs.github.com/rest","status":"401"}
[FAIL] set -euo pipefail
[FAIL] source set_container_versions.sh
[FAIL] env-file generate_html_report.py
[FAIL] if [ "${PRODUCTION}" = "True" ]; then rsync -av "${REPORT_PATH}" "${VM_PATH}"; echo "HTML report copied from $
{REPORT_PATH} to ${VM_PATH}"; fi # return-code=1
2025-06-27T13:45:39Z CRITICAL - failed/ERR