ci: implement a (temporary) workaround to help switching to asciidoctor

We want to switch from using `asciidoctor-extensions` to using regular
`asciidoctor` instead (the custom macros are no longer needed).

To that end, we want to install `mingw-w64-asciidoctor`, but that would fail due
to a conflict with the `mingw-w64-asciidoctor-extensions` package:

  error: failed to commit transaction (conflicting files)
  mingw-w64-x86_64-asciidoctor: /mingw64/bin/asciidoctor exists in filesystem

Let's work around that by explicitly removing the latter package as
needed.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

Diff for: .github/workflows/main.yml

@@ -59,6 +59,15 @@ jobs:
           # reduce time required to install packages by disabling pacman's disk space checking
           sed -i 's/^CheckSpace/#CheckSpace/g' /etc/pacman.conf &&
 
+          # help git-sdk-arm64 switch from `asciidoc` to `asciidoctor`
+          if test mingw-w64-git = '${{ matrix.directory }}'
+          then
+            packages=$(ls -d /var/lib/pacman/local/mingw-w64-*-asciidoctor-extensions-* 2>/dev/null |
+              sed -e 's|.*/||' -e 's|-[0-9].*||)
+            test z "$packages" ||
+            pacman -R --noconfirm $packages
+          fi &&
+
           top_dir=$PWD &&
           cd "${{ matrix.directory }}" &&
           MAKEFLAGS=-j8 makepkg-mingw -s --noconfirm &&