chore(internal/kokoro): skip submodules repeated test if root directo…

…y is already pushd (googleapis#10265)

* chore(internal/kokoro): skip submodules repeated test if root directory is already pushd

* run tests on all changed dirs

internal/kokoro/presubmit.sh

@@ -92,6 +92,13 @@ CHANGED_DIRS=$(echo "$SIGNIFICANT_CHANGES" | tr ' ' '\n' | cut -d/ -f1 | sort -u
 
 echo "Running tests only in changed submodules: $CHANGED_DIRS"
 for d in $CHANGED_DIRS; do
+  # Check if "." is in the list of changed directories, which means the root
+  if [ "$d" = "." ]; then
+    pushd $(dirname $d)
+    runPresubmitTests
+    popd
+    continue
+  fi
   for i in $(find "$d" -name go.mod); do
     pushd $(dirname $i)
     runPresubmitTests