github: work around rustc mingw issue

https://github.com/msys2/MINGW-packages/issues/8732#issuecomment-845079799

.github/workflows/builds.yml

@@ -1379,7 +1379,7 @@ jobs:
         with:
           msystem: MINGW64
           update: true
-          install: git mingw-w64-x86_64-toolchain automake1.16 automake-wrapper autoconf libtool libyaml-devel pcre-devel jansson-devel make mingw-w64-x86_64-libyaml mingw-w64-x86_64-pcre mingw-w64-x86_64-rust mingw-w64-x86_64-jansson unzip p7zip python-setuptools mingw-w64-x86_64-python-yaml mingw-w64-x86_64-jq
+          install: git mingw-w64-x86_64-toolchain automake1.16 automake-wrapper autoconf libtool libyaml-devel pcre-devel jansson-devel make mingw-w64-x86_64-libyaml mingw-w64-x86_64-pcre mingw-w64-x86_64-rust mingw-w64-x86_64-jansson unzip p7zip python-setuptools mingw-w64-x86_64-python-yaml mingw-w64-x86_64-jq mingw-w64-x86_64-libxml2
       # hack: install our own cbindgen system wide as we can't get the
       # preinstalled one to be picked up by configure
       - name: cbindgen