Arm backend: Backend test call setup_path.sh (#14846)

### Summary
This is needed so that the installed FVP can be used from backed tests.
This also add related files to the backed tests trigger script

### Test plan
Arm Backend tests suite

cc @freddan80 @per @oscarandersson8218 @digantdesai

Signed-off-by: Zingo Andersen <[email protected]>

Author: zingo

.ci/scripts/test_backend.sh

@@ -59,6 +59,7 @@ fi
 if [[ "$FLOW" == *arm* ]]; then
     # Setup ARM deps.
     .ci/scripts/setup-arm-baremetal-tools.sh
+    source examples/arm/ethos-u-scratch/setup_path.sh
 
     if [[ "$FLOW" == *ethos_u* ]]; then
         # Prepare a test runner binary that can run on the Corstone-3x0 FVPs

.github/workflows/test-backend-arm.yml

@@ -12,6 +12,9 @@ on:
     paths:
       - .github/workflows/test-backend-arm.yml
       - .github/workflows/_test_backend.yml
+      - .ci/scripts/test_backend.sh
+      - backends/test/suite/flow.py
+      - backends/test/suite/flows/arm.py
   workflow_dispatch:
 
 concurrency: