GitHub Actions: move a few checks around

- use observation that macOS build is much faster, so perform the
  documentation up-to-date check at the end of that job.

- move build & configure Python 2/3 checks in the more appropriate
  secondary checks job

.github/workflows/checks.yml

@@ -36,15 +36,6 @@ jobs:
     - name: binary tests
       run: ./run_tests binaries || { cat testing_binaries.log; false; }
 
-    - name: check command documentation
-      run: ./docs/generate_user_docs.sh && git diff --exit-code docs/
-
-    - name: check configure with Python 3
-      run: python3 ./configure || { cat configure.log; false; }
-
-    - name: check build with Python 3
-      run: ./build -dryrun || { cat build.log; false; }
-
 
 
 
@@ -106,6 +97,8 @@ jobs:
     - name: binary tests
       run: ./run_tests binaries || { cat testing_binaries.log; false; }
 
+    - name: check command documentation
+      run: ./docs/generate_user_docs.sh && git diff --exit-code docs/
 
 
 
@@ -181,3 +174,17 @@ jobs:
     - name: check building of documentation
       run: python3 -m sphinx -n -N -W -w sphinx.log docs/ tmp/
 
+    - name: install build dependencies
+      run: sudo apt-get install clang-8 libqt5opengl5-dev libqt5svg5-dev libglvnd-dev libeigen3-dev zlib1g-dev libfftw3-dev
+
+    - name: check configure with Python 2
+      run: python2 ./configure || { cat configure.log; false; }
+
+    - name: check build with Python 2
+      run: python2 ./build -dryrun || { cat build.log; false; }
+
+    - name: check configure with Python 3
+      run: python3 ./configure || { cat configure.log; false; }
+
+    - name: check build with Python 3
+      run: python3 ./build -dryrun || { cat build.log; false; }