pw_build: Fix configs in pw_rust_executable

Bug: 343111481

Fix issue that configs forwared from invoker are overwriten.

Change-Id: I7c0a7cdf5fc9e22e4605378cbb3896dae1adecb8
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/212171
Reviewed-by: Erik Gilling <konkers@google.com>
Commit-Queue: Jiacheng Lu <lujc@google.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/pw_build/rust_executable.gni b/pw_build/rust_executable.gni
index 59a680d..8a41b4e 100644
--- a/pw_build/rust_executable.gni
+++ b/pw_build/rust_executable.gni
@@ -42,9 +42,7 @@
     assert(_edition == "2015" || _edition == "2018" || _edition == "2021",
            "edition ${_edition} is not supported")
 
-    if (defined(invoker.configs)) {
-      configs = invoker.configs
-    } else {
+    if (!defined(configs)) {
       configs = []
     }
     configs += [ "$dir_pw_build:rust_edition_${_edition}" ]