Valgrind test: split and move up list.

Since the valgrind test takes so long it approaches the limit allowed by
github, move it to the head of the list so it's the first one started and
split the longest tests out into a second instance that runs concurrently
with the first.

.github/workflows/c-cpp.yml

@@ -12,22 +12,30 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-16.04, ubuntu-18.04, ubuntu-20.04, macos-10.15, macos-11.0]
-        configs: [default, pam]
+        # First we test all OSes in the default configuration.
+        os: [ubuntu-20.04, ubuntu-18.04, ubuntu-16.04, macos-10.15, macos-11.0]
+        configs: [default]
         # Then we include any extra configs we want to test for specific VMs.
+        # Valgrind slows things down quite a bit, so start them first.
         include:
+          - { os: ubuntu-20.04, configs: valgrind-1 }
+          - { os: ubuntu-20.04, configs: valgrind-2 }
+          - { os: ubuntu-20.04, configs: pam }
           - { os: ubuntu-20.04, configs: kitchensink }
           - { os: ubuntu-20.04, configs: hardenedmalloc }
           - { os: ubuntu-20.04, configs: libressl-head }
           - { os: ubuntu-20.04, configs: openssl-head }
-          - { os: ubuntu-20.04, configs: valgrind }
+          - { os: ubuntu-18.04, configs: pam }
           - { os: ubuntu-18.04, configs: kerberos5 }
           - { os: ubuntu-18.04, configs: libedit }
           - { os: ubuntu-18.04, configs: sk }
           - { os: ubuntu-18.04, configs: selinux }
           - { os: ubuntu-18.04, configs: kitchensink }
           - { os: ubuntu-18.04, configs: without-openssl }
+          - { os: ubuntu-16.04, configs: pam }
           - { os: ubuntu-16.04, configs: kitchensink }
+          - { os: macos-10.15,  configs: pam }
+          - { os: macos-11.0,   configs: pam }
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2