testsuite: daemon-proxy-protocol drop-leg tolerates EPIPE on send

The probe() helper sends the @RSYNCD greeting after the PROXY header, then
reads the daemon's response.  For a `want='drop'` leg (untrusted peer / a
daemon with no `proxy protocol hosts`) the daemon closes the connection,
which on some CI runners surfaces as EPIPE/ECONNRESET on our sendall() before
we ever read -- an uncaught BrokenPipeError that failed the test (seen on
AlmaLinux 8 and Ubuntu 22.04, a timing race; other runners closed read-side).
Wrap the send/recv in `except OSError` and leave `out` empty: for want='drop'
the absent greeting is the expected outcome; want='ok'/'denied' still fail
correctly on an absent greeting.

testsuite/daemon-proxy-protocol_test.py

@@ -115,6 +115,7 @@ def probe(port, hdr, label, *, want):
     """
     s = socket.create_connection(('127.0.0.1', port), timeout=10)
     s.settimeout(10)
+    out = b''
     try:
         if hdr:
             s.sendall(hdr)
@@ -122,7 +123,6 @@ def probe(port, hdr, label, *, want):
         # list-only request.  Protocol 30, no capabilities, no auth.
         s.sendall(b'@RSYNCD: 30.0\nmod\n')
         # Slurp everything the daemon writes before it closes.
-        out = b''
         try:
             s.shutdown(socket.SHUT_WR)
         except OSError:
@@ -135,6 +135,13 @@ def probe(port, hdr, label, *, want):
             if not chunk:
                 break
             out += chunk
+    except OSError:
+        # A 'drop' daemon closes the connection, which can surface as
+        # EPIPE/ECONNRESET on our sendall() before we ever read -- a timing
+        # race seen on some CI runners.  Leave `out` empty and let the
+        # want-check below decide: for want='drop' the absent greeting is the
+        # expected outcome; for want='ok'/'denied' it still fails correctly.
+        pass
     finally:
         s.close()