CI: install autoconf 2.72 before generating release tarballs

This is required for compatibility with GCC 14 and future clang
versions. See e.g. <https://gcc.gnu.org/gcc-14/porting_to.html>
for some background.

.github/workflows/release.yml

@@ -96,6 +96,10 @@ jobs:
           )
           sudo apt-get update
           sudo apt-get install --no-install-recommends "${packages[@]}"
+      - name: "Install autoconf 2.72"   # for compatibility with GCC 14 & clang versions
+        run: |
+          wget https://ftp.gnu.org/gnu/autoconf/autoconf-2.7x2.tar.xz # FIXME: intentional bad URL error
+          tar xvf autoconf-2.72.tar.xz
       - name: "Configure GAP"
         run: dev/ci-configure-gap.sh
       - name: "Build GAP"