Set fetch-depth to 0 to check out all branches and tags

The default is fetch depth 1, which checks out just the given commit. Setting this to 0 lets us build against any branch, without having to have tagged it first. Without this, vanagon throws its hands up because it can't get any version from 'git describe'.

Author: nmburgan

.github/workflows/build_vanagon.yml

@@ -165,6 +165,7 @@ jobs:
         uses: actions/checkout@v5
         with:
           ref: ${{ inputs.ref }}
+          fetch-depth: 0 # So we fetch all history and tags and can build non-tagged versions
 
       - name: Install Cygwin and bootstrap dependencies (Windows only)
         if: ${{ startsWith(matrix.platform, 'windows') }}