[gimp] desktop: update 2.99.8 release date in AppData metadata.

[Jehan <jehanp src gnome org>]

commit 944cbc17e8a25e2624741b844df7816a26fe3398
Author: Jehan <jehan girinstud io>
Date:   Sun Oct 17 15:53:35 2021 +0200

    desktop: update 2.99.8 release date in AppData metadata.

 desktop/org.gimp.GIMP.appdata.xml.in.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/desktop/org.gimp.GIMP.appdata.xml.in.in b/desktop/org.gimp.GIMP.appdata.xml.in.in
index 22a57be60f..18020081b9 100644
--- a/desktop/org.gimp.GIMP.appdata.xml.in.in
+++ b/desktop/org.gimp.GIMP.appdata.xml.in.in
@@ -73,7 +73,7 @@
   </provides>
 
   <releases>
-    <release version="2.99.8" date="TODO" type="development">
+    <release version="2.99.8" date="2021-10-17" type="development">
       <description>
         <_p>
         While during this fourth cycle of development, many efforts were devoted to