Fix resume custom reference link bug (#2941)

Hi,

I noticed an issue where the CV page fails to link to the correct custom
PDF when the `{% unless site.data.resume %}` block is executed in
`cv.liquid`. To resolve this, I updated the code to align its logic with
the else block to make it consistent.

---------

Co-authored-by: Maruan Al-Shedivat <[email protected]>

Author: rickyyuan07

_layouts/cv.liquid

@@ -8,12 +8,17 @@ layout: default
         {{ page.title }}
         {% if page.cv_pdf %}
           <a
-            href="{{ page.cv_pdf | prepend: 'assets/pdf/' | relative_url}}"
+            {% if page.cv_pdf contains '://' %}
+              href="{{ page.cv_pdf }}"
+            {% else %}
+              href="{{ page.cv_pdf | prepend: 'assets/pdf/' | relative_url }}"
+            {% endif %}
             target="_blank"
             rel="noopener noreferrer"
             class="float-right"
-            ><i class="fa-solid fa-file-pdf"></i
-          ></a>
+          >
+            <i class="fa-solid fa-file-pdf"></i>
+          </a>
         {% endif %}
       </h1>
       {% if page.description %}