Remove Linux ARM64 from CI matrix - not available in GitHub Actions

GitHub Actions doesn't provide ubuntu-latest-arm64 runners.
Linux ARM64 builds would require QEMU emulation or Docker multi-platform setup.

Current coverage:
- macOS ARM64 (Apple Silicon)
- macOS x64 (Intel)
- Linux x64
- Windows x64

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

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: rathboma

.github/workflows/electron.yml

@@ -24,9 +24,6 @@ jobs:
           # Linux x64
           - os: ubuntu-latest
             electron-version: '39.2.7'
-          # Linux ARM64
-          - os: ubuntu-latest-arm64
-            electron-version: '39.2.7'
           # Windows x64
           - os: windows-latest
             electron-version: '39.2.7'

.github/workflows/nodejs.yml

@@ -23,9 +23,6 @@ jobs:
           # Linux x64
           - os: ubuntu-latest
             node-version: 22.x
-          # Linux ARM64
-          - os: ubuntu-latest-arm64
-            node-version: 22.x
           # Windows x64
           - os: windows-latest
             node-version: 22.x