Fix release workflow: remove x86_64 macOS target

Remove x86_64-apple-darwin target from release matrix as OpenSSL
cross-compilation fails on macos-latest (ARM) runners.

Keep only:
- x86_64-unknown-linux-gnu (Linux)
- aarch64-apple-darwin (macOS ARM)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: abutlabs

.github/workflows/release.yml

@@ -55,9 +55,6 @@ jobs:
           - os: ubuntu-latest
             target: x86_64-unknown-linux-gnu
             artifact: cargo-polkajam-linux-x86_64
-          - os: macos-latest
-            target: x86_64-apple-darwin
-            artifact: cargo-polkajam-macos-x86_64
           - os: macos-latest
             target: aarch64-apple-darwin
             artifact: cargo-polkajam-macos-aarch64