pw_env_setup: Fix warning when executing bootstrap

Change-Id: Id7644bf801ad99bc1d2d806cfd43dc33d9460473
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/39882
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Keir Mierle <keir@google.com>
diff --git a/pw_env_setup/util.sh b/pw_env_setup/util.sh
index 2c5befa..2a6b584 100644
--- a/pw_env_setup/util.sh
+++ b/pw_env_setup/util.sh
@@ -73,7 +73,7 @@
 
 pw_eval_sourced() {
   if [ "$1" -eq 0 ]; then
-    _PW_NAME=$(basename "$PW_SETUP_SCRIPT_PATH" .sh)
+    _PW_NAME=$(basename "$_BOOTSTRAP_PATH" .sh)
     pw_bold_red "Error: Attempting to $_PW_NAME in a subshell"
     pw_red "  Since $_PW_NAME.sh modifies your shell's environment variables,"
     pw_red "  it must be sourced rather than executed. In particular, "