Setting repository branch when pulling Vulkan-Docs

[oddhack]

@gpx1000 I'd like to configure .github/workflows/ci.yml to use a different branch of Vulkan-Docs while iterating on #121 and it looked like the place to do that was by setting DOC_Commit_Hash.default = 'antora_refpages', but trying this still resulted in pulling main branch (see https://github.com/KhronosGroup/Vulkan-Site/actions/runs/16898073082/job/47871636713#step:7:66 under 'Checking out the ref'). Is this the wrong way of configuring this behavior?

I tried a workaround by just changing to explicit 'ref: antora_refpages' in https://github.com/KhronosGroup/Vulkan-Site/actions/runs/16898158040/job/47871893885#step:7:66 and that seems to be working. So I misunderstand how to configure inputs.DOC_Commit_Hash.default, or the logic for using that to set the ref is not doing what I expect it would.