[FIX] theme_test_custo: correct tour trigger to look for svg images

Since [1], the test "test_01_menu_hierarchies" fails.

Note that the check is not as strong as before as we cannot check the
source of the image.

Since [2], the btn-primary is now btn-secondary
---

[1]: https://github.com/odoo/odoo/commit/3cc5ff6e96493f2b068090f880987def3787895e
[2]: https://github.com/odoo/odoo/commit/eca4d1b1d4ea58959793b0a2cbfa443308759372

runbot-226641

closes odoo/design-themes#1102

Signed-off-by: Robin Lejeune (role) <role@odoo.com>

theme_test_custo/static/src/builder/footer.xml

@@ -7,7 +7,7 @@
         <BuilderSelectItem title.translate="Custom Theme"
                 actionParam="{ view: 'theme_test_custo.template_footer_custom', vars: { 'footer-template': 'custom-theme' } }"
         >
-            <Img src="'/theme_test_custo/static/src/img/template_footer_opt.svg'"/>
+            <Img src="'/theme_test_custo/static/src/img/template_footer_opt.svg'" class="'theme_test_custo_footer'"/>
         </BuilderSelectItem>
     </xpath>
 </t>

theme_test_custo/static/src/builder/header.xml

@@ -16,7 +16,7 @@
                     },
                 ]"
         >
-            <Img src="'/theme_test_custo/static/src/img/template_header_opt.svg'"/>
+            <Img src="'/theme_test_custo/static/src/img/template_header_opt.svg'" class="'theme_test_custo_header'"/>
         </BuilderSelectItem>
     </xpath>
 </t>