[MM-24123] Fix flaky TestGetLinkMetadata (#14654)

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

app/post_metadata_test.go

@@ -12,6 +12,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"os"
 	"strconv"
 	"strings"
 	"testing"
@@ -1872,7 +1873,7 @@ func TestGetLinkMetadata(t *testing.T) {
 		assert.Nil(t, og)
 		assert.Nil(t, img)
 		assert.NotNil(t, err)
-		assert.Contains(t, err.Error(), "Client.Timeout")
+		assert.True(t, os.IsTimeout(err))
 
 		ogFromCache, imgFromCache, ok := getLinkMetadataFromCache(requestURL, timestamp)
 		assert.True(t, ok)