Remove documentation tests from GitHub Actions (#26981)

We moved documentation tests to readthedocs since a while,
so remove the one on GitHub.

share/spack/qa/run-doc-tests

@@ -1,26 +0,0 @@
-#!/bin/bash -e
-#
-# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
-# Spack Project Developers. See the top-level COPYRIGHT file for details.
-#
-# SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-#
-# Description:
-#     Builds Spack documentation and checks for
-#     possible syntax errors. Treats warnings as
-#     fatal errors.
-#
-# Usage:
-#     run-doc-tests
-#
-. "$(dirname $0)/setup.sh"
-check_dependencies sphinx-apidoc sphinx-build dot git hg svn
-
-# Move to documentation directory
-# Allows script to be run from anywhere
-cd "$SPACK_ROOT/lib/spack/docs"
-
-# Treat warnings as fatal errors
-make clean --silent
-make SPHINXOPTS=-W