Fix SlicerSOFA packageupload error

In a superbuild extension, packageupload target is in the inner build folder.

This commit should fix this error:
gmake[3]: *** No rule to make target `packageupload'.  Stop.
(https://slicer.cdash.org/viewBuildError.php?buildid=3623543)

fixes Slicer/SlicerSOFA#31

SlicerSOFA.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://raw.githubusercontent.com/Slicer/Slicer/main/Schemas/slicer-extension-catalog-entry-schema-v1.0.1.json#",
   "build_dependencies": [],
-  "build_subdirectory": ".",
+  "build_subdirectory": "inner-build",
   "category": "Simulation",
   "scm_revision": "main",
   "scm_url": "https://github.com/Slicer/SlicerSOFA",