doc-build.yml: Set NETLIFY_ALIAS to the tag name #33862
Description
From sagemath/documentation#24 (comment)
When the workflow is invoked on GITHUB_REF of the form refs/tags/TAG_NAME, set NETLIFY_ALIAS=TAG_NAME. The resulting URL can then be referred to in a redirect rule. sagemath/documentation#24 (comment)
CC: @tobiasdiez @haraldschilly @dimpase
Component: website/wiki
Author: Matthias Koeppe
Branch/Commit: u/mkoeppe/doc_build_yml__set_netlify_alias_to_the_tag_name @ b786c07
Issue created by migration from https://trac.sagemath.org/ticket/33862