This is happening due to a slight configuration change on the machine that creates Windows builds for https://dolphin-emu.org/download/, and was fixed shortly after 5.0-15260 was built. So, it isn't anything on your end, it's on our end. It doesn't affect Dolphin in any way other than showing that extra "[HEAD]" text in the title bar and showing the branch in the About dialog as "HEAD".
If you want to know the technical details of what happened, we updated to a new version of the buildbot software which uses git checkout instead of git reset, and this ended up resulting in a detached HEAD in git. Can't say I understand the buildbot software well enough to know how the fix actually worked, though
If you want to know the technical details of what happened, we updated to a new version of the buildbot software which uses git checkout instead of git reset, and this ended up resulting in a detached HEAD in git. Can't say I understand the buildbot software well enough to know how the fix actually worked, though