ci: fixup macos workflow

- Attempting to install `pkg-config` or `pkgconf` results in brew
  complaining about conflicts. Rely on whatever version already present.
- macos-14 seemingly needs an explicit libtool install.

.github/workflows/macos_builds.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - name: dependencies
-      run: brew install check cmake help2man libfido2 mandoc pkg-config automake
+      run: brew install check cmake help2man libfido2 mandoc libtool automake
     - name: build
       env:
         CC: ${{ matrix.cc }}