fix: underscore matching not work (#30826)

issue: https://github.com/milvus-io/milvus/issues/30721

Signed-off-by: longjiquan <jiquan.long@zilliz.com>

internal/parser/planparserv2/pattern_match.go

@@ -5,7 +5,7 @@ import (
 )
 
 var wildcards = map[byte]struct{}{
-	// '_': {}, // TODO
+	'_': {},
 	'%': {},
 }
 

internal/parser/planparserv2/pattern_match_test.go

@@ -121,6 +121,12 @@ func Test_translatePatternMatch(t *testing.T) {
 			wantOperand: "prefix%suffix",
 			wantErr:     false,
 		},
+		{
+			args:        args{pattern: "_0"},
+			wantOp:      planpb.OpType_Match,
+			wantOperand: "_0",
+			wantErr:     false,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {