Configure coverage helpers for the test exec group (#292)

These tools run on the test action's execution platform and should thus be configured for it.

Closes #292

COPYBARA_INTEGRATE_REVIEW=#292 from fmeum:fix-coverage-exec-group d341fc0
PiperOrigin-RevId: 755287580
Change-Id: I88548701af955d6ffe410852f60d8b6337f44d81

Author: fmeum

java/bazel/rules/bazel_java_test.bzl

@@ -86,14 +86,14 @@ java_test(
         BASE_BINARY_ATTRS,
         {
             "_lcov_merger": attr.label(
-                cfg = "exec",
+                cfg = config.exec(exec_group = "test"),
                 default = configuration_field(
                     fragment = "coverage",
                     name = "output_generator",
                 ),
             ),
             "_collect_cc_coverage": attr.label(
-                cfg = "exec",
+                cfg = config.exec(exec_group = "test"),
                 allow_single_file = True,
                 default = "@bazel_tools//tools/test:collect_cc_coverage",
             ),