Add the (no-op) 'exec_groups' attribute to the rule() function.

Currently not linked up to any logic behind the scenes. Usage of attribute hidden behind new --experimental_execution_groups flag.

PiperOrigin-RevId: 302672390
diff --git a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
index 6a183e8..d3d2e05 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
@@ -139,6 +139,7 @@
         "--incompatible_allow_tags_propagation=" + rand.nextBoolean(), // flag, Java names differ
         "--experimental_cc_shared_library=" + rand.nextBoolean(),
         "--experimental_repo_remote_exec=" + rand.nextBoolean(),
+        "--experimental_exec_groups=" + rand.nextBoolean(),
         "--incompatible_always_check_depset_elements=" + rand.nextBoolean(),
         "--incompatible_applicable_licenses=" + rand.nextBoolean(),
         "--incompatible_depset_for_libraries_to_link_getter=" + rand.nextBoolean(),
@@ -193,6 +194,7 @@
         .experimentalAllowTagsPropagation(rand.nextBoolean())
         .experimentalCcSharedLibrary(rand.nextBoolean())
         .experimentalRepoRemoteExec(rand.nextBoolean())
+        .experimentalExecGroups(rand.nextBoolean())
         .incompatibleAlwaysCheckDepsetElements(rand.nextBoolean())
         .incompatibleApplicableLicenses(rand.nextBoolean())
         .incompatibleDepsetForLibrariesToLinkGetter(rand.nextBoolean())