upgrades: Use inline SVG icons

Tests:

- All the icons appear as before in both light/dark themes.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/upgrades/templates/backports-firstboot.html

@@ -6,6 +6,7 @@
 {% load bootstrap %}
 {% load i18n %}
 {% load static %}
+{% load plinth_extras %}
 
 {% block content %}
   <h1>{% trans "Frequent Feature Updates" %}</h1>
@@ -31,7 +32,7 @@
 
   <div class="alert alert-warning d-flex align-items-center" role="alert">
     <div class="me-2">
-      <span class="fa fa-exclamation-triangle" aria-hidden="true"></span>
+      {% icon 'exclamation-triangle' %}
       <span class="visually-hidden">{% trans "Caution:" %}</span>
     </div>
     <div>

plinth/modules/upgrades/templates/upgrades-dist-upgrade-confirm.html

@@ -6,6 +6,7 @@
 {% load bootstrap %}
 {% load i18n %}
 {% load static %}
+{% load plinth_extras %}
 
 {% block content %}
   <h3>{% trans "Confirm Distribution Update?" %}</h3>
@@ -13,7 +14,7 @@
   {% if status.next_action == "manual" %}
     <div class="alert alert-danger d-flex align-items-center" role="alert">
       <div class="me-2">
-        <span class="fa fa-exclamation-triangle" aria-hidden="true"></span>
+        {% icon 'exclamation-triangle' %}
         <span class="visually-hidden">{% trans "Caution:" %}</span>
       </div>
 

plinth/modules/upgrades/templates/upgrades-dist-upgrade.html

@@ -42,7 +42,7 @@
     {% if not status.updates_enabled or not status.dist_upgrade_enabled or not status.has_free_space or not status.current_codename %}
       <div class="alert alert-warning d-flex align-items-center" role="alert">
         <div class="me-2">
-          <span class="fa fa-exclamation-triangle" aria-hidden="true"></span>
+          {% icon 'exclamation-triangle' %}
           <span class="visually-hidden">{% trans "Caution:" %}</span>
         </div>
 

plinth/modules/upgrades/templates/upgrades_configure.html

@@ -80,7 +80,7 @@
   {% if can_activate_backports and not is_backports_requested %}
     <div class="alert alert-warning d-flex align-items-center" role="alert">
       <div class="me-2">
-        <span class="fa fa-exclamation-triangle" aria-hidden="true"></span>
+        {% icon 'exclamation-triangle' %}
         <span class="visually-hidden">{% trans "Caution:" %}</span>
       </div>
       <div>