Fix protocol_version_mismatch race condition in 3.1.3 golden file

When rsync 3.1.3 outputs protocol mismatch errors, the sender and
receiver processes may write concurrently without proper newline
separation, resulting in concatenated messages like:
  "(see the rsync man page for an explanation)protocol version mismatch..."

Convert the two separate expected messages into a message_group that
accepts:
- Individual messages (when output is properly separated)
- Concatenated forms (when race condition occurs)

This allows the interop validation to pass regardless of which timing
behavior occurs during the test.

Author: oferchen

tests/interop/messages/golden-3.1.3.toml

@@ -18,13 +18,20 @@ text = "rsync error: syntax or usage error (code 1) at main.c(1601) [client]"
 role = "client"
 scenario = "invalid_option"
 
-[[messages]]
-text = "protocol version mismatch -- is your shell clean?"
-scenario = "protocol_version_mismatch"
-
-[[messages]]
-text = "(see the rsync man page for an explanation)"
+# Race-dependent: The protocol mismatch messages may appear separately or concatenated
+# due to concurrent output from sender/receiver processes
+[[message_groups]]
+name = "protocol_mismatch_description"
 scenario = "protocol_version_mismatch"
+require_at_least = 1
+messages = [
+    # Individual messages when output is properly separated
+    { text = "protocol version mismatch -- is your shell clean?" },
+    { text = "(see the rsync man page for an explanation)" },
+    # Concatenated forms when race condition causes no newline between messages
+    { text = "(see the rsync man page for an explanation)protocol version mismatch -- is your shell clean?" },
+    { text = "protocol version mismatch -- is your shell clean?(see the rsync man page for an explanation)" },
+]
 
 # Race-dependent: At least one protocol/IPC error must appear
 [[message_groups]]