gh-bc/tests: run tests in parallel

Helps to mitigate failures due to timeout in CI on emulated architectures:
https://ci.freebsd.org/job/FreeBSD-main-riscv64-test/16565/testReport/usr.bin.gh-bc/

MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D59547

usr.bin/gh-bc/tests/bc_tests.sh

@@ -2,4 +2,4 @@
 unset LC_ALL LC_CTYPE LC_MESSAGES LC_MONETARY LC_NUMERIC LC_TIME
 export LANG=C
 export BC_TEST_OUTPUT_DIR=${PWD}
-exec "$(dirname "$(realpath "$0")")"/tests/all.sh -n bc 1 1 0 0 bc
+exec "$(dirname "$(realpath "$0")")"/tests/all.sh bc 1 1 0 0 bc

usr.bin/gh-bc/tests/dc_tests.sh

@@ -2,4 +2,4 @@
 unset LC_ALL LC_CTYPE LC_MESSAGES LC_MONETARY LC_NUMERIC LC_TIME
 export LANG=C
 export BC_TEST_OUTPUT_DIR=${PWD}
-exec "$(dirname "$(realpath "$0")")"/tests/all.sh -n dc 1 1 0 0 dc
+exec "$(dirname "$(realpath "$0")")"/tests/all.sh dc 1 1 0 0 dc