Error not annotated on github due to invalid span

When the conversion to a github annotation fails, the error is still mentioned in the summary, but not visible as an annoation.
I guess the conversion could be more lenient, and fall back to reporting on the manifest if the span is invalid.

See: https://github.com/typst/packages/pull/4596/checks?check_run_id=72651830265

We should probably also log the diagnostic, like we do when run in the CLI:

2026-04-23T16:19:21.140300Z ERROR typst_package_check::cli: failed to print diagnostics (failed to load file (is a directory))
2026-04-23T16:19:21.140330Z ERROR typst_package_check::cli: Raw diagnostics: [
    Diagnostic {
        severity: Error,
        code: Some(
            "exclude/template",
        ),
        message: "This file is part of the template and should not be excluded.",
        labels: [
            Label {
                style: Primary,
                file_id: /examples,
                range: 0..0,
                message: "",
            },
        ],
        notes: [],
    },
]

Start with the GitHub annotation conversion and the CLI diagnostic-reporting path, using the linked check run and the shown raw diagnostic as references. Trace how an invalid span is handled and how the manifest is reported; done means the summary error remains visible, a manifest-level annotation is produced, and the diagnostic is logged.