Add cases for non-compliant struct tag

Add test cases to decode_test.go and encode_test.go that cover an
edge case described in issue #157 where a struct field uses an
incorrect tag syntax (a bare string like `bar` without the `yaml:`
prefix) alongside a correct `yaml:"foo"` tag. The new tests assert
that the library continues to accept and round-trip values when one
field uses the supported-but-nonstandard tag form.

This clarifies expected behavior and prevents regressions for legacy
struct tags that some users rely on.

Author: SVilgelm

decode_test.go

@@ -960,6 +960,19 @@ ba?r: a?bc
 			"ba?r": "a?bc",
 		},
 	},
+
+	// issue #157
+	{
+		`foo: foo
+bar: bar`,
+		struct {
+			F string `yaml:"foo"` // correct tag, because it has yaml prefix
+			B string `bar`        //nolint:govet // incorrect tag, but supported
+		}{
+			F: "foo",
+			B: "bar",
+		},
+	},
 }
 
 type M map[string]any

encode_test.go

@@ -582,6 +582,18 @@ var marshalTests = []struct {
 		},
 		"foo:\n    bar: a?bc\n",
 	},
+
+	// issue $157
+	{
+		struct {
+			F string `yaml:"foo"` // the correct tag
+			B string `bar`        // the incorrect tag, but supported
+		}{
+			F: "foo",
+			B: "bar",
+		},
+		"foo: foo\nbar: bar\n",
+	},
 }
 
 func TestMarshal(t *testing.T) {