git_pack: add Git pack test file

This file was created by running:

    mkdir testrepo
    cd testrepo
    git init
    git config --local author.name "Test User"
    git config --local author.email "testuser@testhost"
    git config --local committer.name "Test User"
    git config --local committer.email "testuser@testhost"
    gunzip -c ~/hachoir/tests/files/test.txt.gz > test.txt
    git add test.txt
    TZ= faketime '2025-01-06 10:00:00' git commit -m "add test.txt"
    cp ~/hachoir/tests/files/vim.lnk .
    echo "This is another line" >> test.txt
    git add .
    TZ= faketime '2025-01-06 10:01:00' git commit -m "add another line, and add binary file"
    git gc
    cp .git/objects/pack/pack-31c691f659cbc7841ca55a26a342fdaf0b89c533.pack ~/hachoir/tests/files/

(using Git 2.34.1)