[FIX] theme_*: remove mb-2 class on orphan buttons

*: anelusia, artists, aviato, graphene, kiddo, loftspace, monglia,
notes, odoo_experts, paptic, test_custo, yes

The community PR [125824] introduces an automatic check on buttons to
add the `mb-2` class when several buttons follow each other, so that
they have space to breathe when split on multiple lines.
For consistency, this commit therefore removes most `mb-2` occurrences
on buttons within themes as long as they are alone on their line, but
keeps or adds the class when several buttons are next to each other.

[125824]: https://github.com/odoo/odoo/pull/125824

task-3369604

closes odoo/design-themes#680

Related: odoo/odoo#125824
Signed-off-by: Benjamin Vray (bvr) <bvr@odoo.com>

theme_loftspace/views/snippets/s_call_to_action.xml

@@ -27,6 +27,9 @@
     <xpath expr="//div[hasclass('col-lg-12')]/p" position="attributes">
         <attribute name="style" add="text-align: center;" remove="text-align: right;" separator=";"/>
     </xpath>
+    <xpath expr="//a[hasclass('btn')]" position="attributes">
+        <attribute name="class" add="mb-2" separator=" "/>
+    </xpath>
     <!-- Add secondary button -->
     <xpath expr="//a[hasclass('btn')]" position="before">
         <a href="#" class="btn btn-secondary btn-lg me-2 mb-2">Our services</a>