Disable excessive GH Actions builds

[jriwanek]

Summary

Disable stable building on github actions, it doesn't provide any benefit and people should be using the ci builds, not actions builds anyway, they just slow down actions building. Left them in incase they're needed in future though.
Fix silly derp and restore linux actions building again.

Checklist

• Closes #xxx
• I have discussed this with core contributors already
• This pull request requires changes to the ROM set
  • I have opened a roms pull request - https://github.com/86Box/roms/pull/changeme/

References

Provide links to datasheets or other documentation that helped you implement this pull request.