Fix screen reader issue on profile page.

lms/static/sass/features/_learner-profile.scss

@@ -371,6 +371,7 @@
       @extend %t-ultrastrong;
 
       display: inline-block;
+      color: #222;
     }
 
     .subheader {

openedx/features/learner_profile/templates/learner_profile/learner_profile.html

@@ -36,7 +36,7 @@ from openedx.core.djangolib.markup import HTML
             </div>
             % if own_profile:
                 <div class="profile-header">
-                    <div class="header">${_("My Profile")}</div>
+                    <h2 class="header">${_("My Profile")}</h2>
                     <div class="subheader">
                         ${_('Build out your profile to personalize your identity on {platform_name}.').format(
                             platform_name=platform_name,