Workaround the sandbox is missing files bug

For some reason multiplex sandboxing seems to have issues with files
going missing. It's been happening for a while, but intermittently. It
got much worse recently.

Not sure if this is a rule set bug or a Bazel bug. Regardless, disabling
multiplex sandboxing fixes it.

.bazelrc_shared

@@ -22,7 +22,10 @@ build --strategy=worker,sandboxed,local
 
 build --worker_max_instances=4
 build --worker_sandboxing
-build --experimental_worker_multiplex_sandboxing
+# Disable multiplex sandboxing because there is a bug that causes files which
+# should be in the sandbox to not be. Not sure if this is a Bazel bug or a rule
+# set bug. Something we need to deal with either way.
+#build --experimental_worker_multiplex_sandboxing
 build --experimental_worker_cancellation
 build --verbose_failures