unrelated: parallel build for CI

Author: nmwsharp

.github/workflows/linux.yml

@@ -25,7 +25,7 @@ jobs:
       run: cd test && mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Debug -DPOLYSCOPE_BACKEND_OPENGL3_GLFW=ON -DPOLYSCOPE_BACKEND_OPENGL_MOCK=ON ..
 
     - name: build
-      run: cd test/build && make
+      run: cd test/build && make -j4
 
     - name: run test mock backend
       run: cd test/build && ./bin/polyscope-test --gtest_catch_exceptions=0 backend=openGL_mock
@@ -54,7 +54,7 @@ jobs:
       run: cd test && mkdir build && cd build && cmake -DBUILD_SHARED_LIBS=TRUE -DCMAKE_BUILD_TYPE=Debug -DPOLYSCOPE_BACKEND_OPENGL3_GLFW=ON -DPOLYSCOPE_BACKEND_OPENGL_MOCK=ON -DPOLYSCOPE_BACKEND_OPENGL3_EGL=ON ..
 
     - name: build
-      run: cd test/build && make
+      run: cd test/build && make -j4
 
     - name: run test mock backend
       run: cd test/build && ./bin/polyscope-test --gtest_catch_exceptions=0 backend=openGL_mock