Update bcr presubmit tasks to reside in side a module.

PiperOrigin-RevId: 775008719

Author: mollyibot

.bcr/presubmit.yml

@@ -1,25 +1,14 @@
-matrix:
-  platform:
-    - ubuntu2004
-    - macos
-  bazel:
-    - 8.x
-tasks:
-  guava_sample_build_test:
-    platform: ${{ platform }}
-    bazel: ${{ bazel }}
-    build_targets:
-      - '//...'
-    working_directory: samples/guava
-  helloworld_sample_test:
-    platform: ${{ platform }}
-    bazel: ${{ bazel }}
-    test_targets:
-      - '//...'
-    working_directory: samples/helloworld
-  wasm_sample_test:
-    platform: ${{ platform }}
-    bazel: ${{ bazel }}
-    test_targets:
-      - '//...'
-    working_directory: samples/wasm
+bcr_test_module:
+  module_path: "samples/helloworld"
+  matrix:
+    platform:
+      - ubuntu2004
+      - macos
+    bazel:
+      - 8.x
+  tasks:
+    helloworld_sample_test:
+      platform: ${{ platform }}
+      bazel: ${{ bazel }}
+      test_targets:
+        - '//...'