CI: Fix ci_lib and test_lib have_<cmd>() when <cmd> exits abnormally

We were not raising CalledProcessError when exit status != 0.

.ci/ci_lib.py

@@ -58,6 +58,7 @@ def _have_cmd(args):
     try:
         subprocess.run(
             args, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
+            check=True,
         )
     except OSError as exc:
         if exc.errno == errno.ENOENT:

tests/testlib.py

@@ -160,6 +160,7 @@ def _have_cmd(args):
     try:
         subprocess.run(
             args, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
+            check=True,
         )
     except OSError as exc:
         if exc.errno == errno.ENOENT: