[FIX] website: prevent crash due to color-mix in Safari 16.5

__Current behavior before commit:__
The `color` attribute of `hr` is set to `$hr-color`[1].
`$hr-color` is equal to `$border-color`[2] which itself is equal to
`--o-border-color`[3].
Finally `--o-border-color` is set using `fade-currentColor()`[4]
which uses the `color-mix` css function on `currentColor`[5].

In short, the `color` of `hr` depends on itself. This creates a circular
reference that makes Safari 16.5 crash.

This bug is caused by WebKit. There seems to be a commit to fix[6]
this bug but it looks like it was not backported to this version of
Safari.

__Description of the fix:__
Set `border-top` color of `hr` to `$border-color`. This way of doing
gives the same result as setting `color` but removes the circular
dependency with `currentColor` that makes Safari 16.5 crash.

`color` is set to `inherit` to override the bootstrap rule[1] that
leads to the bug.

For reference, `hr` color is already set like that here[7].

__Steps to reproduce the issue on runbot:__
1. Go to the website shop using Safari 16.5
2. Add an item to the cart
3. Open the cart view
4. Safari crashes

opw-3806725

[1]: https://github.com/odoo/odoo/blob/1154556/addons/web/static/lib/bootstrap/scss/_reboot.scss#L71
[2]: https://github.com/odoo/odoo/blob/1154556/addons/website/static/src/scss/bootstrap_overridden.scss#L333
[3]: https://github.com/odoo/odoo/blob/1154556/addons/website/static/src/scss/bootstrap_overridden.scss#L91
[4]: https://github.com/odoo/odoo/blob/1154556/addons/website/static/src/scss/website.scss#L35
[5]: https://github.com/odoo/odoo/blob/1154556/addons/website/static/src/scss/primary_variables.scss#L2219
[6]: https://github.com/WebKit/WebKit/commit/0d0b884
[7]: https://github.com/odoo/odoo/blob/1154556/addons/website/static/src/snippets/s_hr/000.scss#L7

Part-of: odoo/odoo#160495
Co-authored-by: qsm-odoo <qsm@odoo.com>

addons/website/static/src/scss/website.scss

@@ -406,6 +406,21 @@ $-header-nav-link-height: $nav-link-height;
     }
 }
 
+hr {
+    // Move the set up color as a border color. Indeed, we may use color-mix to
+    // define that color as a function of currentColor, in which case
+    // Safari 16.5 is known to crash when using that to set the color property.
+    border-top: $hr-height solid $hr-color;
+    color: inherit;
+    // FIXME before the commit that introduced this background-color the color
+    // of HR was the superposition of:
+    // - background-color = currentColor = see below
+    // - color = $hr-color = transparent mix of currentColor
+    // => So a transparent version of the inherited color, on top of itself
+    // => This line makes it so this stays the same for now.
+    background-color: $hr-color;
+}
+
 h2 {
     color: map-get($colors, 'o-cc1-h2');
 }

addons/website/static/src/snippets/s_hr/000.scss

@@ -3,10 +3,12 @@
     line-height: 0;
     hr {
         padding: 0;
+        // TODO we already change the way the color is applied (using a border)
+        // in website.css. In master, we should just let that system work the
+        // way it is and not force something here.
         border: 0;
         border-top: 1px solid $border-color;
         margin: 0;
-        color: inherit;
         // As BS5 added "opacity" and "background-color" on hr tag, we remove
         // that here to let users set the color as they want.
         opacity: 1;