feat(etl): update Enemy Territory: Legacy to 2.78.1

[jobhh]

Description

Fixes #3683 after the 2.78.1 archive is uploaded to http://linuxgsm.download/WolfensteinEnemyTerritory/etlegacy-v2.78.1-i386-et-260b.tar.xz

Sidenote: I noticed in the archive currently used contains files that I think are not required. This is the original 2.78.1 file with the required pk3 files added to etmain and some icon, metainfo, etc files removed that aren't required for a server. Similar to the 2.77.1 files created previously.

Type of change

• Bug fix (a change which fixes an issue).
• New feature (change which adds functionality).
• New Server (new server added).
• Refactor (restructures existing code).
• Comment update (typo, spelling, explanation, examples, etc).

Checklist

PR will not be merged until all steps are complete.

• This pull request links to an issue.
• This pull request uses the develop branch as its base.
• This pull request Subject follows the Conventional Commits standard.
• This code follows the style guidelines of this project.
• I have performed a self-review of my code.
• I have checked that this code is commented where required.
• I have provided a detailed with enough description of this PR.
• I have checked If documentation needs updating.

Documentation

If documentation does need updating either update it by creating a PR (preferred) or request a documentation update.

• User docs: https://github.com/GameServerManagers/LinuxGSM-Docs
• Dev docs: https://github.com/GameServerManagers/LinuxGSM-Dev-Docs

[github-actions]

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