ci/deqp-runner: remove duplicate values to avoiding read the same file multiple times

Some jobs define multiple of these to the same value; let's simply
ignore those, as they might have a legitimate reason to do it.

This wasn't a problem with skips and flakes as those can contain
duplicates, but fails (next commit) are not allowed to be defined
multiple times.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36648>

.gitlab-ci/deqp-runner.sh

@@ -74,10 +74,11 @@ add_if_exists() {
   fi
 }
 
-for prefix in \
-  "$DRIVER_NAME" \
-  "$GPU_VERSION" \
-  ; do
+# remove duplicate values to avoid reading the same file multiple times
+{
+  echo "$DRIVER_NAME"
+  echo "$GPU_VERSION"
+} | sort -u | while read -r prefix; do
   add_if_exists "$prefix" flakes
   add_if_exists "$prefix" skips
 done