project.py: pass --recurse-submodules={value}

If submodules is False, explicitly pass '=no'.  Uninitialized submodules
may cause the default option to fail.

Change-Id: Ia00bcba5b69c4b65195f4c469c686a3ef9a4a3ad
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/330159
Reviewed-by: Xin Li <delphij@google.com>
Tested-by: LaMont Jones <lamontjones@google.com>
diff --git a/project.py b/project.py
index 41e81d1..ff91d18 100644
--- a/project.py
+++ b/project.py
@@ -2142,8 +2142,7 @@
     if prune:
       cmd.append('--prune')
 
-    if submodules:
-      cmd.append('--recurse-submodules=on-demand')
+    cmd.append(f'--recurse-submodules={"on-demand" if submodules else "no"}')
 
     spec = []
     if not current_branch_only: