ci: split ci.yml into a test workflow and a build test workflow (#22302)

Having a workflow that only builds neovim without running all of the
tests is a cheap way to test the build still works without burning too
much CI time.

.github/actions/cache/action.yml

@@ -18,5 +18,5 @@ runs:
       with:
         path: ${{ env.DEPS_BUILD_DIR }}
         key: ${{ env.CACHE_KEY }}-${{ hashFiles('cmake**', 'ci/**',
-          '.github/workflows/ci.yml', 'CMakeLists.txt',
+          '.github/workflows/test.yml', 'CMakeLists.txt',
           'runtime/CMakeLists.txt', 'src/nvim/**/CMakeLists.txt') }}