build: stop rebuilding the Flatpak dependencies on every run (#15501)

scripts/flatpak/com.orcaslicer.OrcaSlicer.yml

@@ -144,6 +144,7 @@ modules:
       env:
         BUILD_DIR: deps/build_flatpak
     build-commands:
+      - tar xf deps.tar
       - |
         cmake -S deps -B $BUILD_DIR \
           -DFLATPAK=ON \
@@ -169,10 +170,10 @@ modules:
       - /libpython/include
 
     sources:
-      # OrcaSlicer deps/ directory (avoids copying .git from worktree)
-      - type: dir
-        path: ../../deps
-        dest: deps
+      # flatpak-builder cannot checksum a directory, so a `type: dir` here would
+      # rebuild every dependency on every run. Generated by make_deps_tar.sh.
+      - type: file
+        path: deps.tar
 
       # ---------------------------------------------------------------
       # Pre-downloaded dependency archives