fix: false kernel update reports when linux-image-generic meta-package is installed

[mhrznamn068]

Problem

Hosts running Ubuntu 22.04 with linux-image-generic (the GA meta-package) installed were incorrectly reported by patchman as having an available kernel update to the HWE series (e.g. linux-image-6.8.0-106-generic) even though apt upgrade would never offer it.

Root cause

find_deb_kernel_updates extracts the kernel series (e.g. 5.15) from each installed kernel package name to avoid cross-track comparisons (GA vs HWE). For meta-packages like linux-image-generic, get_deb_kernel_series() returns None because the name contains no version number. The series guard was if installed_series is not None, so meta-packages bypassed it entirely.

Additionally, processed_prefixes marks the linux-image- prefix as consumed by the meta-package, preventing the versioned package (linux-image-5.15.0-176-generic) from being processed later with the correct 5.15 series. The net result: the highest linux-image-*-generic in the repo regardless of kernel series was reported as an update.

Fix

When get_deb_kernel_series() returns None for a meta-package, fall back to parsing the series from self.kernel (the running kernel string). This ensures the series guard always runs, correctly excluding packages from a different kernel track.

[furlongm]

Nice find!

This might be a simpler approach?

if installed_series is None:
    continue
processed_prefixes.add(prefix)

[mhrznamn068]

Nice find!

This might be a simpler approach?

if installed_series is None:
    continue
processed_prefixes.add(prefix)

Agreed, simpler approach. Updated.