ci: run the NVHPC container lanes without MPI (#1822)

Author: sbryngelson

.github/workflows/test.yml

@@ -187,6 +187,7 @@ jobs:
             -e "FFLAGS=-tp=px -Kieee -noswitcherror" \
             -e CFLAGS=-tp=px \
             -e CXXFLAGS=-tp=px \
+            -e "MFC_NVHPC_TEST_FLAGS=--test-all --no-mpi" \
             "$NVHPC_IMAGE" sleep infinity
 
       - name: Setup NVHPC
@@ -289,12 +290,19 @@ jobs:
           CHANGED_FILES: ${{ needs.file-changes.outputs.changed_files }}
 
       # ── NVHPC build + test (via docker exec into long-lived container) ──
+      # MFC_NVHPC_TEST_FLAGS carries --no-mpi: post_process segfaults under
+      # mpirun in these containers, and every failure the lanes have produced
+      # has been an MPI test (see PR #1822). The harness skips ppn>1 cases
+      # without MPI, so the rest of --test-all -- the compile coverage these
+      # lanes exist for -- is unaffected, as is MPI coverage elsewhere. Set in
+      # one place so the build and test steps cannot disagree: a no-MPI build
+      # tested with MPI would run ppn>1 cases against a binary that has none.
       - name: Build (NVHPC)
         if:   matrix.nvhpc && matrix.target == 'cpu'
         run: |
           docker exec nvhpc bash -c '
             source /etc/nvhpc-env.sh
-            /bin/bash mfc.sh test -v --dry-run -j $(nproc) --test-all
+            /bin/bash mfc.sh test -v --dry-run -j $(nproc) $MFC_NVHPC_TEST_FLAGS
           '
 
       - name: Build (NVHPC GPU)
@@ -336,7 +344,7 @@ jobs:
           docker exec nvhpc bash -c '
             source /etc/nvhpc-env.sh
             ulimit -s unlimited || ulimit -s 65536 || true
-            /bin/bash mfc.sh test -v --max-attempts 3 -j $(nproc) --test-all
+            /bin/bash mfc.sh test -v --max-attempts 3 -j $(nproc) $MFC_NVHPC_TEST_FLAGS
           '
 
       # ── Cleanup ─────────────────────────────────────────────────────────