[MNT] add slavik57 as a maintenance contributor for fixing `conda-f…

…orge` `sktime-all-extras 0.28.0` release (#6308)

Add myself as a maintenance contributor as was kindly invited by
@fkiraly here:
#6304 (comment)

.all-contributorsrc

@@ -2774,6 +2774,15 @@
         "code",
         "doc"
       ]
+    },
+    {
+      "login": "slavik57"
+      "name": "Slava Shpitalny"
+      "avatar_url": "https://avatars.githubusercontent.com/u/6184997?v=4",
+      "profile": "https://github.com/slavik57",
+      "contributions": [
+        "maintenance"
+      ]
     }
   ]
 }