[feature] Support incoming avatar/header descriptions (#4275)

Signed-off-by: nicole mikołajczyk <git@mkljczk.pl>

# Description

Follow-up to #4270

Closes https://codeberg.org/superseriousbusiness/gotosocial/issues/3450

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [ ] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4275
Co-authored-by: nicole mikołajczyk <git@mkljczk.pl>
Co-committed-by: nicole mikołajczyk <git@mkljczk.pl>

internal/federation/dereferencing/account_test.go

@@ -28,6 +28,7 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"strings"
 	"testing"
 	"time"
 
@@ -473,6 +474,49 @@ func (suite *AccountTestSuite) TestRefreshFederatedRemoteAccountWithKeyChange()
 	suite.True(updatedAcc.PublicKey.Equal(fetchingAcc.PublicKey))
 }
 
+func (suite *AccountTestSuite) TestDereferenceRemoteAccountWithAvatarDescription() {
+	ctx, cncl := context.WithCancel(suite.T().Context())
+	defer cncl()
+
+	fetchingAcc := suite.testAccounts["local_account_1"]
+	remoteURI := "https://shrimpnet.example.org/users/shrimp"
+	description := "me scrolling fedi on a laptop, there's a monster ultra white and another fedi user on my right."
+
+	// Fetch the remote account to load into the database.
+	remoteAcc, _, err := suite.dereferencer.GetAccountByURI(ctx,
+		fetchingAcc.Username,
+		testrig.URLMustParse(remoteURI),
+		false,
+	)
+	suite.NoError(err)
+	suite.NotNil(remoteAcc)
+
+	suite.Equal(remoteAcc.AvatarMediaAttachment.Description, description)
+
+	remotePerson := suite.client.TestRemotePeople[remoteURI]
+
+	description = strings.TrimSuffix(description, ".")
+
+	icon := remotePerson.GetActivityStreamsIcon()
+	image := icon.Begin().GetActivityStreamsImage()
+	nameProp := streams.NewActivityStreamsNameProperty()
+	nameProp.AppendXMLSchemaString(description)
+	image.SetActivityStreamsName(nameProp)
+	icon.SetActivityStreamsImage(0, image)
+	remotePerson.SetActivityStreamsIcon(icon)
+
+	updatedAcc, apAcc, err := suite.dereferencer.RefreshAccount(ctx,
+		fetchingAcc.Username,
+		remoteAcc,
+		remotePerson,
+		nil,
+	)
+
+	suite.NoError(err)
+	suite.NotNil(apAcc)
+	suite.Equal(updatedAcc.AvatarMediaAttachment.Description, description)
+}
+
 func TestAccountTestSuite(t *testing.T) {
 	suite.Run(t, new(AccountTestSuite))
 }