tracing/selftests: Remove exec permissions from trace_marker.tc test

The tests in the selftests should not have the exec permissions set. The
trace_marker.tc test accidentally was committed with the exec permission.

Set the permission to that file back to just read/write.

No functional nor code changes.

Link: https://lore.kernel.org/linux-trace-kernel/[e-mail]/

Signed-off-by: Steven Rostedt (Google) <[e-mail]>