setup.py: use {version_b} to calculate mupdf download URL instead of hard-coding.

Author: julian-smith-artifex-com

setup.py

@@ -425,7 +425,7 @@ def get_mupdf_internal(out, location=None, sha=None, local_tgz=None):
     log(f'get_mupdf_internal(): {out=} {location=} {sha=}')
     assert out in ('dir', 'tgz')
     if location is None:
-        location = 'https://mupdf.com/downloads/archive/mupdf-1.24.10-source.tar.gz'
+        location = f'https://mupdf.com/downloads/archive/mupdf-{version_b}-source.tar.gz'
         #location = 'git:--branch master https://github.com/ArtifexSoftware/mupdf.git'
 
     if location == '':