Add "_id" string to linter exceptions (FerretDB#1364)

In this PR "_id" constant was removed and linter settings were tweaked to not trigger a warning.

.golangci.yml

@@ -185,3 +185,7 @@ issues:
     # that's a valid usage of bson.D
     - linters: [govet]
       text: "`go.mongodb.org/mongo-driver/bson/primitive.E` composite literal uses unkeyed fields"
+
+    # we don't want to introduce that constant
+    - linters: [goconst]
+      text: "^string `_id` has \\d+ occurrences, make it a constant"

internal/types/document.go

@@ -23,11 +23,6 @@ import (
 	"github.com/FerretDB/FerretDB/internal/util/must"
 )
 
-const (
-	// The idKey is key for _id field.
-	idKey = "_id"
-)
-
 // Common interface with bson.Document.
 //
 // TODO Remove this type.
@@ -187,7 +182,7 @@ func (d *Document) Command() string {
 //
 // As a special case, _id always becomes the first key.
 func (d *Document) add(key string, value any) error {
-	if key == idKey {
+	if key == "_id" {
 		// ensure that _id is the first field
 		d.fields = slices.Insert(d.fields, 0, field{key, value})
 	} else {
@@ -230,7 +225,7 @@ func (d *Document) Set(key string, value any) {
 		panic(fmt.Sprintf("types.Document.Set: key is duplicated: %s", key))
 	}
 
-	if key == idKey {
+	if key == "_id" {
 		// ensure that _id is the first field
 		if i := slices.Index(d.Keys(), key); i >= 0 {
 			d.fields = slices.Delete(d.fields, i, i+1)

internal/types/document_validation.go

@@ -89,7 +89,7 @@ func (d *Document) ValidateData() error {
 		}
 		duplicateChecker[key] = struct{}{}
 
-		if key == idKey {
+		if key == "_id" {
 			idPresent = true
 		}
 
@@ -108,7 +108,7 @@ func (d *Document) ValidateData() error {
 				return err
 			}
 		case *Array:
-			if key == idKey {
+			if key == "_id" {
 				return newValidationError(ErrWrongIDType, fmt.Errorf("The '_id' value cannot be of type array"))
 			}
 
@@ -129,7 +129,7 @@ func (d *Document) ValidateData() error {
 					}
 				case *Array:
 					return newValidationError(ErrValidation, fmt.Errorf(
-						"invalid value: { %q: %v } (nested arrays are not allowed)", key, FormatAnyValue(v),
+						"invalid value: { %q: %v } (nested arrays are not supported)", key, FormatAnyValue(v),
 					))
 				}
 			}
@@ -141,7 +141,7 @@ func (d *Document) ValidateData() error {
 				)
 			}
 		case Regex:
-			if key == idKey {
+			if key == "_id" {
 				return newValidationError(ErrWrongIDType, fmt.Errorf("The '_id' value cannot be of type regex"))
 			}
 		}

internal/types/document_validation_test.go

@@ -76,7 +76,7 @@ func TestDocumentValidateData(t *testing.T) {
 				"_id", "1",
 				"foo", must.NotFail(NewArray("bar", must.NotFail(NewArray("baz")))),
 			)),
-			reason: errors.New(`invalid value: { "foo": [ "bar", [ "baz" ] ] } (nested arrays are not allowed)`),
+			reason: errors.New(`invalid value: { "foo": [ "bar", [ "baz" ] ] } (nested arrays are not supported)`),
 		},
 		"NestedDocumentNestedArray": {
 			doc: must.NotFail(NewDocument(
@@ -85,7 +85,7 @@ func TestDocumentValidateData(t *testing.T) {
 					"bar", must.NotFail(NewArray("baz", must.NotFail(NewArray("qaz")))),
 				)),
 			)),
-			reason: errors.New(`invalid value: { "bar": [ "baz", [ "qaz" ] ] } (nested arrays are not allowed)`),
+			reason: errors.New(`invalid value: { "bar": [ "baz", [ "qaz" ] ] } (nested arrays are not supported)`),
 		},
 		"ArrayDocumentNestedArray": {
 			doc: must.NotFail(NewDocument(
@@ -96,7 +96,7 @@ func TestDocumentValidateData(t *testing.T) {
 					)),
 				)),
 			)),
-			reason: errors.New(`invalid value: { "bar": [ "baz", [ "qaz" ] ] } (nested arrays are not allowed)`),
+			reason: errors.New(`invalid value: { "bar": [ "baz", [ "qaz" ] ] } (nested arrays are not supported)`),
 		},
 	} {
 		name, tc := name, tc