[FIX] purchase: no request for quotation views won't overlap dropdown

Steps to reproduce:

- Go to Request for quotation.
- Make any search that retrieves no values. (So we get the "no request
for quotation found." message)
- Open Filters dropdown menu. (or Any menu which lenghts will be over
this message)

Issue:

The dropdown menu will be under the message, the message is overlaping
the dropdown menu when it shouldn't be.

Solution:

We need to set the message to `position: relative` instead of
`position: static` so we take into account the right z-index for the
message.

opw-3080171

closes odoo/odoo#107409

X-original-commit: 47a6a555c5bcedffdfda7586ecbe4311d2a45e5f
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>
Signed-off-by: Maruan Aguerdouh Mohtar (magm) <magm@odoo.com>

addons/purchase/static/src/views/purchase_listview.scss

@@ -1,3 +1,3 @@
 .o_rfq_no_content {
-    position: static;
+    position: relative;
 }