Add conditional gobject-introspection workaround for macOS x86_64 CI builds

[Copilot]

This PR adds a targeted workaround for macOS x86_64 (Intel) CI builds by pre-installing gobject-introspection from source before the main dependency installation step.

Changes Made

• Added a new step "Pre-install gobject-introspection from source (x86 only)" to the build-macOS-x86_64 job
• Uses the conditional if: runner.arch == 'X64' to ensure the step only runs on Intel Mac runners
• Positioned the step after the homebrew fix and before the main dependency installation
• The Apple Silicon build job remains unchanged to avoid unnecessary overhead

Why This Change Is Needed

This workaround addresses build issues specific to macOS x86_64 runners where gobject-introspection may need to be built from source to work correctly with other dependencies. By using the architecture-specific conditional, we ensure:

• Intel Mac builds get the necessary workaround
• Apple Silicon builds remain efficient without unnecessary steps
• The CI pipeline is more robust and targeted

The step will only execute on x86_64 runners, keeping Apple Silicon builds streamlined and efficient.

This pull request was created as a result of the following prompt from Copilot chat.

Update the C/C++ CI workflow fix so that the workaround step for pre-installing 'gobject-introspection' from source only runs on macOS x86_64 (Intel) runners. Use GitHub Actions' conditional 'if: runner.arch == "X64"' to ensure the step is skipped for Apple Silicon (arm64) builds. The step should look like:

• name: Pre-install gobject-introspection from source (x86 only)
  if: runner.arch == 'X64'
  run: brew install --build-from-source gobject-introspection

This will avoid unnecessary workarounds on Apple Silicon and keep builds efficient.

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