go.mod: bump github.com/getkin/kin-openapi to v0.131.0

As deepmap/oapi-codegen didn't work with this newer version, upgrade to
oapi-codegen/oapi-codegen v2.

Mitigating CVE-2025-30153

vendor/github.com/getkin/kin-openapi/openapi3/example_validation.go

@@ -0,0 +1,16 @@
+package openapi3
+
+import "context"
+
+func validateExampleValue(ctx context.Context, input any, schema *Schema) error {
+	opts := make([]SchemaValidationOption, 0, 2)
+
+	if vo := getValidationOptions(ctx); vo.examplesValidationAsReq {
+		opts = append(opts, VisitAsRequest())
+	} else if vo.examplesValidationAsRes {
+		opts = append(opts, VisitAsResponse())
+	}
+	opts = append(opts, MultiErrors())
+
+	return schema.VisitJSON(input, opts...)
+}