Fix(packages): Add detection path for Linglong on Debian, issue #1898

[GuilingQiyu]

This PR resolves an issue where Linglong packages were not detected on Debian 13 systems when installed from the official repository provided by the Deepin team.

Fixes #1898

Problem

The original detection logic only checked for Linglong packages in the /var/lib/linglong/repo/refs/heads/main directory. However, on Debian 13 with Linglong installed from Deepin's repo, the packages are located in /var/lib/linglong/repo/refs/remotes/stable/main.

Solution

This change adds a fallback check. It first attempts to count packages in the original heads/main path. If the count is zero, it then checks the remotes/stable/main path. This ensures compatibility with both installation methods.

Verification

[100%] Built target fastfetch
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 `$$b      "-.__               OS: Debian GNU/Linux 13 (trixie) x86_64
  `Y$$b                        Host: ASUS TUF Gaming A15 FA506QM_FA506QM (1.0)
   `Y$$.                       Kernel: Linux 6.12.38+deb13-amd64
     `$$b.                     Uptime: 2 hours, 12 mins
       `Y$$b.                  Packages: 3369 (dpkg), 11 (flatpak), 2 (linglong)
         `"Y$b._               Shell: bash 5.2.37
             `""""             Display (NE156QHM-NY1): 2560x1440 @ 60 Hz in 16" [Built-in]
                               DE: KDE Plasma 6.3.6
                               WM: KWin (Wayland)
                               WM Theme: Breeze
                               Theme: Breeze (Dark) [Qt], Breeze-Dark [GTK2], Breeze [GTK3]
                               Icons: breeze-dark [Qt], breeze-dark [GTK2/3/4]
                               Font: Noto Sans (10pt) [Qt], Noto Sans (10pt) [GTK2/3/4]
                               Cursor: breeze (24px)
                               Terminal: code 1.103.1
                               CPU: AMD Ryzen 7 5800H (16) @ 4.46 GHz
                               GPU 1: NVIDIA GeForce RTX 3060 Mobile / Max-Q [Discrete]
                               GPU 2: AMD Radeon Vega Series / Radeon Vega Mobile Series []
                               Memory: 8.38 GiB / 58.77 GiB (14%)
                               Swap: 0 B / 1024.00 MiB (0%)
                               Disk (/): 108.27 GiB / 223.00 GiB (49%) - ext4
                               Disk (/media/glqyu/Data): 1.76 TiB / 1.85 TiB (95%) - ntfs3

                               Battery (A32-K55): 100% [AC Connected]
                               Locale: zh_CN.UTF-8

The fix is confirmed to work on my system.