ci: don't use make -j, which is currently buggy

Author: mgates3

.github/workflows/make.yml

@@ -37,9 +37,10 @@ jobs:
     - name: Build ScaLAPACK
       run: |
         cp SLmake.inc.example SLmake.inc
-        make --silent -j lib
-        make --silent all
-        
+        # make -j is buggy; see #54.
+        make lib
+        make all
+
     - name: Run examples
       working-directory: ${{github.workspace}}/EXAMPLE
       run: |