tools: use -f in mkosi summary in fetch-distro.py

$ ./tools/fetch-distro.py -u fedora
+ mkosi --json -d fedora summary
‣ Ignoring --distribution from the CLI. Run with -f to rebuild the image with this setting

Follow-up for 35f6e5c327

tools/fetch-distro.py

@@ -35,7 +35,7 @@ def parse_args():
     return p.parse_args()
 
 def read_config(distro: str):
-    cmd = ['mkosi', '--json', '-d', distro, 'summary']
+    cmd = ['mkosi', '--json', '-d', distro, '-f', 'summary']
     if args.profile:
         cmd += ['--profile', args.profile]
     print(f"+ {shlex.join(cmd)}")