tests(bcr): Set Bazel version in BCR presubmit config. (bazel-contrib#1753)

BCR now requires the presubmit configs to specify the Bazel versions to
run tests with. Without this, the BCR checks fail and we can't do
releases to BCR.

Author: rickeylev

.bcr/presubmit.yml

@@ -16,9 +16,11 @@ bcr_test_module:
   module_path: "examples/bzlmod"
   matrix:
     platform: ["debian11", "macos", "ubuntu2004", "windows"]
+    bazel: [6.x, 7.x]
   tasks:
     run_tests:
       name: "Run test module"
       platform: ${{ platform }}
+      bazel: ${{ bazel }}
       test_targets:
         - "//..."