[FIX] web: fix the animation of the rainbow man

Before this commit, the animation of the rainbow, in the rainbow man
component, didn't work well in Firefox and Safari.
After this commit, this animation works well in every modern browsers.

task-2742831

Part-of: odoo/odoo#83403

addons/web/static/src/core/effects/rainbow_man.scss

@@ -46,8 +46,8 @@
 
   .o_reward_rainbow {
     path {
-      stroke-dasharray: 600;
-      stroke-dashoffset: 0;
+      stroke-dasharray: 600 600;
+      stroke-dashoffset: -600;
       fill: none;
       stroke-linecap: round;
       stroke-width: 21px;
@@ -211,17 +211,17 @@
 }
 
 @keyframes reward-rainbow {
-  0% {
-    stroke-dashoffset: -500;
-  }
   to {
     stroke-dashoffset: 0;
   }
 }
 
 @keyframes reward-rainbow-reverse {
+  from {
+    stroke-dashoffset: 0;
+  }
   to {
-    stroke-dashoffset: -500;
+    stroke-dashoffset: -600;
   }
 }