projects-dir.mk: Add diff-projects target

The diff-all and diff targets diff all projects in the workspace
without filtering.

Add a target "diff-projects". It sets PGIT_SH_PROJECTS to the list of
projects from build-order, limiting the diff to the dependency
closure around $(PROJECTS).

Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/ec/ssh/AsyncSSH.py

@@ -215,7 +215,7 @@ class AsyncSSH(Base):
                     return
                 if proc.stdin is not None:
                     proc.stdin.write(data)
-                await proc.stdin.drain()
+                    await proc.stdin.drain()
 
         async def _pump_stdout() -> None:
             while True: