tests/shell: Fix shellcheck SC1090 to handle the location of sourced files

tests/shell: Fix shellcheck SC1090 to handle the location of sourced files

Running shellcheck on some of the shell scripts throws
below error:

	In tests/shell/coresight/unroll_loop_thread_10.sh line 8:
	. "$(dirname $0)"/../lib/coresight.sh
	  ^-- SC1090: Can't follow non-constant source. Use a directive to specify location.

This happens on shellcheck version "0.6.0". Fix shellcheck
warning for SC1090 using "shellcheck source="i option to mention
the location of sourced files.

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Tested-by: Ian Rogers <irogers@google.com>
Reviewed-by: Kajol Jain <kjain@linux.ibm.com>
Cc: maddy@linux.ibm.com
Cc: disgoel@linux.vnet.ibm.com
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230907171540.36736-2-atrajeev@linux.vnet.ibm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>