fix(workflows): fix workflow syntax errors, revert Alpine, and enable PR builds

[d0ugal]

Changes

This PR fixes workflow syntax errors, Alpine 3.23.0 qemu emulation issues, and enables PR builds:

1. Fixed workflow syntax errors:

   • Changed default-branch to target-branch for googleapis/release-please-action@v4
   • Removed invalid continue-on-error input from docker/build-push-action@v6

2. Fixed Alpine 3.23.0 qemu emulation issues:

   • Reverted final stage from alpine:3.23.0 to alpine:3.22.2
   • Changed builder stage from golang:1.25.5-alpine to golang:1.25.4-alpine (uses Alpine 3.22.2)

3. Enhanced dev-build workflow:

   • Added pull_request trigger to build on PRs
   • Only push images on push events to main, not on PRs
   • Skip GHCR login on PRs since we're not pushing

Errors Fixed

• Unexpected input(s) 'default-branch' for release-please-action
• Unexpected input(s) 'continue-on-error' for build-push-action
• ARM64 build failures with Alpine 3.23.0 qemu emulation

Testing

Once merged, workflows should complete successfully and PRs will validate builds without pushing images.