Upstream provides no ABI stability across updates, hence we always need to rebuild mupdf even for patch version upgrades. Previously only the major + minor version was encoded in the SONAME (e.g. mupdf-1.23). This is insufficient as apk's dependency tracker will then not update dependency on partial upgrades.
This changeset also removes the libmupdf.so.1.23 symlink and
only provides libmupdf.so → libmupdf.so.1.23.3.