Relax result type validation to avoid nightly build failure

This commit fixes the string result type validation, PR tektoncd#4779 adds
result type and asumes that the default type should be string via
mutating webhook. PR tektoncd#4818 adds the validation for this. However,
resources that did already exist in etcd didn't get the default. So this
commit relaxes this validation.

Author: Yongxuanzhang

pkg/apis/pipeline/v1beta1/result_types.go

@@ -25,7 +25,7 @@ type TaskResult struct {
 
 	// Description is a human-readable description of the result
 	// +optional
-	Description string `json:"description"`
+	Description string `json:"description,omitempty"`
 }
 
 // TaskRunResult used to describe the results of a task

pkg/apis/pipeline/v1beta1/result_validation.go

@@ -31,9 +31,5 @@ func (tr TaskResult) Validate(ctx context.Context) (errs *apis.FieldError) {
 		return errs.Also(ValidateEnabledAPIFields(ctx, "results type", config.AlphaAPIFields))
 	}
 
-	if tr.Type != ResultsTypeString {
-		return apis.ErrInvalidValue(tr.Type, "type", fmt.Sprintf("type must be string"))
-	}
-
 	return nil
 }

pkg/apis/pipeline/v1beta1/task_validation_test.go

@@ -1226,21 +1226,6 @@ func TestTaskSpecValidateError(t *testing.T) {
 			Paths:   []string{"results[0].name"},
 			Details: "Name must consist of alphanumeric characters, '-', '_', and must start and end with an alphanumeric character (e.g. 'MyName',  or 'my-name',  or 'my_name', regex used for validation is '^([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9]$')",
 		},
-	}, {
-		name: "result type not validate",
-		fields: fields{
-			Steps: validSteps,
-			Results: []v1beta1.TaskResult{{
-				Name:        "MY-RESULT",
-				Type:        "wrong",
-				Description: "my great result",
-			}},
-		},
-		expectedError: apis.FieldError{
-			Message: `invalid value: wrong`,
-			Paths:   []string{"results[0].type"},
-			Details: "type must be string",
-		},
 	}, {
 		name: "context not validate",
 		fields: fields{