[ruff] Remove stale PPC64 release target (#29221)

Release signing fails while collecting `powerpc64-unknown-linux-gnu`
wheels because the target remains in `dist-workspace.toml` after #22766
removed its builds. Remove the stale entry so the signing inventory
matches the release build matrix.

Co-authored-by: Zanie Blue <contact@zanie.dev>

dist-workspace.toml

@@ -28,7 +28,6 @@ targets = [
     "armv7-unknown-linux-gnueabihf",
     "armv7-unknown-linux-musleabihf",
     "x86_64-apple-darwin",
-    "powerpc64-unknown-linux-gnu",
     "powerpc64le-unknown-linux-gnu",
     "riscv64gc-unknown-linux-gnu",
     "s390x-unknown-linux-gnu",