first crack at making bundled dependencies optional

.github/workflows/cmake.yml

@@ -3,6 +3,7 @@ name: CMake
 on:
   push:
     paths:
+    - ".github/workflows/cmake.yml"
     - "src/**"
     - "ext/**"
     - "CMakeLists.txt"
@@ -22,7 +23,7 @@ jobs:
         - { name: "Windows MSVC x86", os: windows-latest, artifact: windows-x86, arch: x86 }
         - { name: "Windows MSVC x64", os: windows-latest, artifact: windows-x64 }
         - { name: "Windows MSVC ARM64", os: windows-latest, artifact: windows-arm64, arch: amd64_arm64 }
-        - { name: "Ubuntu", artifact: "linux", os: ubuntu-latest }
+        - { name: "Ubuntu", artifact: "linux", os: ubuntu-latest, extra: "-DUSE_BUNDLED_ZSTD:BOOL=OFF" }
     runs-on: ${{matrix.config.os}}
 
     steps:
@@ -34,6 +35,11 @@ jobs:
       if: ${{startsWith(matrix.config.os, 'windows')}}
       with:
         arch: ${{matrix.config.arch && matrix.config.arch || 'x64'}}
+    - uses: awalsh128/cache-apt-pkgs-action@latest
+      if: ${{matrix.config.artifact == 'linux'}}
+      with:
+        packages: libzstd-dev
+        version: 1.0
 
     - name: Configure CMake
       run: >-