🤖 perf: skip code signing in PR/merge_group builds for parallel macOS builds

The macOS build was taking 24+ minutes because code signing was enabled
for merge_group events (condition was 'event_name != pull_request').
This forced sequential x64+arm64 builds to avoid keychain race conditions.

Changed the condition to only enable signing for workflow_dispatch (manual
testing). PRs and merge_group now build both architectures in parallel.

- Before: 24m40s (sequential with signing)
- After: ~4m (parallel, no signing)

Releases still get proper signing via release.yml (triggered by tag publish).

Generated with mux

Author: ibetitsmike

.github/workflows/build.yml

@@ -18,11 +18,11 @@ jobs:
 
       - uses: ./.github/actions/setup-mux
 
-      # Skip signing setup for PRs - electron-builder skips signing anyway,
-      # but setting CSC_LINK forces our Makefile to build sequentially.
-      # Without CSC_LINK, x64 and arm64 build in parallel (~90s savings).
+      # Only sign for workflow_dispatch (manual testing of signing process).
+      # PRs and merge_group skip signing - releases use release.yml instead.
+      # Without CSC_LINK, x64 and arm64 builds run in parallel (~12 min faster).
       - name: Setup code signing
-        if: github.event_name != 'pull_request'
+        if: github.event_name == 'workflow_dispatch'
         run: ./scripts/setup-macos-signing.sh
         env:
           MACOS_CERTIFICATE: ${{ secrets.MACOS_CERTIFICATE }}
@@ -32,7 +32,7 @@ jobs:
           AC_APIKEY_ISSUER_ID: ${{ secrets.AC_APIKEY_ISSUER_ID }}
 
       - name: Verify signing setup
-        if: github.event_name != 'pull_request'
+        if: github.event_name == 'workflow_dispatch'
         run: |
           if [ -n "${CSC_LINK:-}" ]; then
             echo "✅ Code signing enabled"