selftests: lib: add prime_numbers.sh test to Makefile

prime_numbers.sh is not included in TEST_PROGS. Add it.
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

tools/testing/selftests/lib/Makefile

@@ -3,6 +3,6 @@
 # No binaries, but make sure arg-less "make" doesn't trigger "run_tests"
 all:
 
-TEST_PROGS := printf.sh bitmap.sh
+TEST_PROGS := printf.sh bitmap.sh prime_numbers.sh
 
 include ../lib.mk