ci: Test cmake_minimum_required

Ensures project configures with 3.13 since it's very easy to
write code that doesn't respect the minimum.

.github/workflows/gtest-ci.yml

@@ -11,7 +11,7 @@ permissions:
   contents: read
 
 jobs:
-  Linux:
+  Linux-Bazel:
     runs-on: ubuntu-latest
     steps:
 
@@ -22,7 +22,24 @@ jobs:
     - name: Tests
       run: bazel test --cxxopt=-std=c++14 --features=external_include_paths --test_output=errors ...
 
-  macOS:
+  Linux-CMake-Min:
+    runs-on: ubuntu-latest
+    steps:
+
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - uses: lukka/get-cmake@latest
+        with:
+          cmakeVersion: 3.13.0
+
+      - name: Configure
+        run: cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -G "Ninja"
+      - name: Build
+        run: cmake --build build
+
+  macOS-Bazel:
     runs-on: macos-latest
     steps:
 
@@ -34,7 +51,7 @@ jobs:
       run:  bazel test --cxxopt=-std=c++14 --features=external_include_paths --test_output=errors ...
 
 
-  Windows:
+  Windows-Bazel:
     runs-on: windows-latest
     steps: