conditionally load RC file with new flag

ci/bazel9.bazelrc

diff --git a/ci/bazel9.bazelrc b/ci/bazel9.bazelrc
new file mode 100644
index 0000000..4d70285
--- /dev/null
+++ b/ci/bazel9.bazelrc
@@ -0,0 +1 @@
+build --incompatible_exclude_starlark_flags_from_exec_config

ci/common.bazelrc

diff --git a/ci/common.bazelrc b/ci/common.bazelrc
index 3b8849a..a19b7af 100644
--- a/ci/common.bazelrc
+++ b/ci/common.bazelrc
@@ -53,7 +53,7 @@
 build --incompatible_sandbox_hermetic_tmp
 build --incompatible_top_level_aspects_require_providers
 build --incompatible_use_cc_configure_from_rules_cc
-build --incompatible_exclude_starlark_flags_from_exec_config
+try-import-if-bazel-version >=9.0.0 %workspace%/ci/bazel9.bazelrc
 
 # We cannot yet build successfully with the following flags:
 #   --incompatible_check_testonly_for_output_files