packaging: use anonymous HTTPS clone URL in PKGBUILD source

The source fragment used git+ssh://git@gitbutter.xyz, which requires the
maintainer's SSH key — so no one else could build peerspeak-git. The repo
is public on gitbutter, so switch to the anonymous HTTPS clone URL.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packaging/PKGBUILD

@@ -14,7 +14,7 @@ optdepends=('pixelpass: screen sharing inside a room'
 provides=('peerspeak')
 conflicts=('peerspeak')
 options=('!lto' '!debug')
-source=("$_pkgname::git+ssh://git@gitbutter.xyz/mollusk/peerspeak.git")
+source=("$_pkgname::git+https://gitbutter.xyz/mollusk/peerspeak.git")
 sha256sums=('SKIP')
 
 pkgver() {