Tell tests (e.g. particularly canbench) to "show their true colors". …

…What this literally does is sets the CLICOLOR_FORCE environment variable to true. This is a convention that different programs follow. In particular, the colored Rust library uses it (and canbench uses colored).

bazel/conf/.bazelrc.build

@@ -141,3 +141,8 @@ common --remote_download_all
 # This option (in conjunction with remote cache issues) creates build failures
 #   https://github.com/bazelbuild/bazel/issues/22387
 common --noexperimental_inmemory_dotd_files
+
+# This is particularly helpful for canbench, but other tests that follow this
+# convention would also benefit. If the test does not support this, this "almost
+# certainly" does no harm.
+test --test_env=CLICOLOR_FORCE=true