Fix typo in test environment check.

PiperOrigin-RevId: 466452738
diff --git a/kokoro/run_tests.sh b/kokoro/run_tests.sh
index 96ec3dc..8b81f3f 100755
--- a/kokoro/run_tests.sh
+++ b/kokoro/run_tests.sh
@@ -86,7 +86,7 @@
     run_linux_tests "python"
 
     local -a MANUAL_TOOLS_TARGETS
-    if [[ -n "{KOKORO_ROOT}" ]]; then
+    if [[ -n "${KOKORO_ROOT}" ]]; then
       MANUAL_TOOLS_TARGETS+=(
         "//testing/cc:aws_kms_aead_test"
         "//testing/cc:gcp_kms_aead_test"