Just: flush the account of what runs before a child writes over it

`error` says why already: the streams are buffered differently when they are
not both a terminal. The same holds where a child inherits this process' stdout,
and there it was missed, so off a terminal the buffer flushed at exit and every
account of what was about to run landed after the output it described. Visible
only in redirected runs, which is to say in logs and never interactively.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: redsun82

misc/just/forward_command.py

@@ -317,6 +317,9 @@ def report_opted_out(command, justfiles, *, ran):
 
 def invoke_just(cwd, args):
     """Run just with the given arguments."""
+    # This process' stdout is block-buffered off a terminal, while the child writes to the
+    # same descriptor at once: without this the account lands after what it describes.
+    sys.stdout.flush()
     try:
         subprocess.run([JUST, *args], check=True, cwd=cwd)
     except subprocess.CalledProcessError as e: