[ROCm][CI] Fix backslash-continuation in pytest marker re-quoting and treat exit code 5 as success (#35798)

Signed-off-by: Andreas Karatzas <akaratza@amd.com>

.buildkite/scripts/hardware_ci/run-amd-test.sh

@@ -99,6 +99,15 @@ is_multi_node() {
   return 1
 }
 
+handle_pytest_exit() {
+  local exit_code=$1
+  if [ "$exit_code" -eq 5 ]; then
+    echo "Pytest exit code 5 (no tests collected) - treating as success."
+    exit 0
+  fi
+  exit "$exit_code"
+}
+
 ###############################################################################
 # Pytest marker/keyword re-quoting
 #
@@ -135,8 +144,9 @@ re_quote_pytest_markers() {
   local collecting=false
   local marker_buf=""
 
-  # Flatten newlines for consistent tokenization
-  local flat="${input//$'\n'/ }"
+  # Strip backslash-newline continuations, then flatten remaining newlines
+  local flat="${input//$'\\\n'/ }"
+  flat="${flat//$'\n'/ }"
 
   # Disable globbing to prevent *.py etc. from expanding during read -ra
   local restore_glob
@@ -164,6 +174,9 @@ re_quote_pytest_markers() {
 
       local is_boundary=false
       case "$word" in
+        # Line-continuation artifact
+        "\\")
+          is_boundary=true ;;
         # Command separators
         "&&"|"||"|";"|"|")
           is_boundary=true ;;
@@ -204,6 +217,9 @@ re_quote_pytest_markers() {
         if [[ "$word" == "-m" || "$word" == "-k" ]]; then
           output+="${word} "
           collecting=true
+        # Drop stray backslash tokens silently
+        elif [[ "$word" == "\\" ]]; then
+          :
         else
           output+="${word} "
         fi
@@ -453,7 +469,9 @@ if is_multi_node "$commands"; then
     done
 
     /bin/bash -c "${composite_command}"
+    exit_code=$?
     cleanup_network
+    handle_pytest_exit "$exit_code"
   else
     echo "Multi-node job detected but failed to parse bracket command syntax."
     echo "Expected format: prefix ; [node0_cmd1, node0_cmd2] && [node1_cmd1, node1_cmd2]"
@@ -480,4 +498,7 @@ else
     --name "${container_name}" \
     "${image_name}" \
     /bin/bash -c "${commands}"
+
+  exit_code=$?
+  handle_pytest_exit "$exit_code"
 fi