selftests/damon: fix damon selftests by installing _common.sh

_common.sh was recently introduced but is not installed and then triggers
an error when trying to run the damon selftests:

selftests: damon: sysfs.sh
./sysfs.sh: line 4: _common.sh: No such file or directory

Install this file to avoid this error.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 511914506d19 ("selftests/damon: introduce _common.sh to host shared function")
Signed-off-by: Alexandre Ghiti <[e-mail]>
Tested-by: Sang-Heon Jeon <[e-mail]>
Reviewed-by: SeongJae Park <[e-mail]>
Tested-by: Enze Li <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/damon/Makefile

···
 
 TEST_FILES = _damon_sysfs.py
 TEST_FILES += drgn_dump_damon_status.py
+TEST_FILES += _common.sh
 
 # functionality tests
 TEST_PROGS += sysfs.sh