chore(demos): restore exec bit on injection/diagnostic scripts

Four host-side helper scripts lost their executable bit somewhere along
the way:

  demos/sensor_diagnostics/inject-fault-scenario.sh
  demos/sensor_diagnostics/run-diagnostics.sh
  demos/moveit_pick_place/arm-self-test.sh
  demos/moveit_pick_place/planning-benchmark.sh

README and run-demo.sh both reference them as ./script.sh, so running
the demos as documented hits "Permission denied". chmod +x to restore
the bit; no content change.

Author: bburda