Make bugzilla-scraping code more robust

[badboy]

We just now had CI issues due to two bugs filed in bugzilla with the metric-expiry-alert whiteboard tag:

• https://bugzilla.mozilla.org/show_bug.cgi?id=1862765
• https://bugzilla.mozilla.org/show_bug.cgi?id=1862764

(see also my comment)

The test failed with:

        probes_with_bugs = {}
        for bug in found_bugs:
            if (
>               re.search(r"release: \[?version (\d+)", bug["description"]).group(1)
                != version
            ):
E           AttributeError: 'NoneType' object has no attribute 'group'

because the bug description did not have version 120 in there. It might be enough to make that check more robust and check for the none case.