👷 Cache cmake for min-req CI (#267)

The CMake min-req CI action takes ages to complete which is really annoying if you have to wait for it to finish in addition to wasting compute ressources. Turns out the vast majority of its time is spent building cmake every time, which is clearly not necessary. This change updates the workflow to cache the built cmake version and restore it if needed cutting ~7.5 minutes of the build.

Author: Thalhammer

.github/workflows/cmake.yml

@@ -73,16 +73,30 @@ jobs:
           cmake --build .
 
   min-req:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
+    env:
+      RUN_ON: ubuntu-20.04
+      CMAKE_URL: https://cmake.org/files/v3.14/cmake-3.14.7.tar.gz
+      CMAKE_VERSION: 3.14.7
     steps:
       - uses: actions/checkout@v2
-      - name: install cmake
-        run: |
-          wget https://cmake.org/files/v3.14/cmake-3.14.7.tar.gz
-          tar -zxf cmake-3.14.7.tar.gz
-          cd cmake-3.14.7
+      - name: Cache CMake
+        id: cache-cmake
+        uses: actions/cache@v3
+        with:
+          path: cmake-${{ env.CMAKE_VERSION }}
+          key: ubuntu-20.04-${{ github.job }}-cmake-${{ env.CMAKE_VERSION }}
+      - name: Build cmake
+        if: steps.cache-cmake.outputs.cache-hit != 'true'
+        run: |
+          wget ${{ env.CMAKE_URL }}
+          tar -zxf cmake-${{ env.CMAKE_VERSION }}.tar.gz
+          cd cmake-${{ env.CMAKE_VERSION }}
           ./bootstrap
           make -j $(nproc)
+      - name: Install cmake
+        run: |
+          cd cmake-${{ env.CMAKE_VERSION }}
           sudo make install
 
       - uses: ./.github/actions/install/gtest