[FIX] web_tour: force tooltip content font style

Force tooltip content font style (size, family, line-height, weight)
so that it does not depend on where the tooltip is in the DOM.

This fixes a problem where the style changed when opening/closing the
tooltip. Indeed, the content dimensions, computed in javascript when
the tooltip is closed were wrong because of the style and the opening
/ closing rely on these values.

addons/web_tour/static/src/less/tip.less

@@ -104,6 +104,12 @@
         transition: visibility 0s ease 0s;
         color: black;
 
+        // Force style so that it does not depend on where the tooltip is attached
+        line-height: @line-height-base;
+        font-size: @font-size-base;
+        font-family: @font-family-sans-serif;
+        font-weight: normal;
+
         .o_skip_tour {
             display: inline-block;
             margin-top: 4px;