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/20231222112831.4c7fa500@gandalf.local.home/

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

tracing/selftests: Add test to test the trace_marker

Add a test that writes longs strings, some over the size of the sub buffer
and make sure that the entire content is there.

Link: https://lore.kernel.org/linux-trace-kernel/20231213111527.6a4c9b58@gandalf.local.home

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>