macOS syntax checks report an unmatched quote in a formula patch

Symptom: ./tests/ci.sh macos fails in patch-homebrew-mesa.sh or patch-homebrew-systemd.sh with unexpected EOF while looking for matching a single quote, although the same scripts pass Linux checks.

Cause: Bash 3.2 misparses the embedded Python heredoc inside command substitution. Quoting the outer assignment does not resolve this parser failure. A newer Bash on Linux does not reproduce it.

Confirm: run /bin/bash -n install/patch-homebrew-mesa.sh and /bin/bash -n install/patch-homebrew-systemd.sh on macOS. These commands parse the files without installing packages or changing formulas.

Fix: update the checkout. Each patch now puts its Python heredoc in a shell function and captures that function’s output. Formula transformations and Linux-only execution remain the same. The macOS CI mode explicitly validates with /bin/bash and runs both formula fixture suites under its constrained system PATH, even when Homebrew Bash is installed.

See the Mesa source, systemd source, and Bash’s heredoc reference.