ci(test): remove the .git directory for Linux

Tests should not rely on being run inside a git clone, so the Linux
builds cover this use case. The macOS builds will continue running with
the .git directory so there's still unix-ish coverage within a git
clone.

.github/workflows/test.yml

@@ -145,6 +145,10 @@ jobs:
           sudo cpanm -n Neovim::Ext || cat "$HOME/.cpanm/build.log"
           perl -W -e 'use Neovim::Ext; print $Neovim::Ext::VERSION'
 
+      - name: Remove .git directory
+        if: ${{ matrix.build.os == 'ubuntu' }}
+        run: cmake -E rm -rf -- .git
+
       - name: Build third-party deps
         run: |
           cmake -S cmake.deps --preset ci -D CMAKE_BUILD_TYPE=Debug ${{ matrix.build.deps_flags }}