avoid parallel access to lustre on levante

levante has file system problem. currently the workaround is to avoid parallel compilation. but this no guarantee that it works

.ci/bb/levante-dkrz/test.all.gcc

@@ -45,9 +45,9 @@ LDFLAGS="${LDFLAGS}" \
 MPI_LAUNCH="${MPI_LAUNCH}" \
 PKG_CONFIG_PATH="${YAXT_ROOT}/lib/pkgconfig:${PPM_ROOT}/lib/pkgconfig"
 
-make -j8
+make
 
-make -j8 check || { cat tests/test-suite.log; exit 1; }
+make check || { cat tests/test-suite.log; exit 1; }
 
 check_all_tests_passed tests/test-suite.log