Update actions/opex-dashboard-generate/README.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: gunzip

actions/opex-dashboard-generate/README.md

@@ -56,7 +56,7 @@ The action consists of three shell scripts:
 The scripts are designed to work on both GNU/Linux (GitHub Actions runners) and BSD-based systems (macOS):
 
 - Path normalization uses a fallback mechanism that works without the GNU-specific `realpath -m` flag
-- All scripts are compatible with both POSIX-compliant shells and bash
+- All scripts require bash; they are invoked with `shell: bash`, use bash-specific features, and are not guaranteed to work with generic POSIX shells
 
 For local testing on macOS, ensure you have basic POSIX tools available (`bash`, `find`, `grep`, `sed`, `git`, `jq`). Optional tools like `yq` provide enhanced parsing but have graceful fallbacks.