Change “Success Criterion” case from title to sentence in technique template partials (#4900)

Discovered while reviewing #4258.

[Preview](https://deploy-preview-4900--wcag2.netlify.app/understanding/status-messages#:~:text=deems%20sufficient%20for%20meeting%20this%20success%20criterion)

Author: adampage

_includes/understanding/intro/failure.html

@@ -1,3 +1,3 @@
 <p>
-  The following are common mistakes that are considered failures of this Success Criterion by the Accessibility Guidelines Working Group.
+  The following are common mistakes that are considered failures of this success criterion by the Accessibility Guidelines Working Group.
 </p>

_includes/understanding/intro/techniques.html

@@ -1,7 +1,7 @@
 <p>
   Each numbered item in this section represents a technique or combination of techniques
-  that the Accessibility Guidelines Working Group deems sufficient for meeting this Success Criterion.
-  A technique may go beyond the minimum requirement of the criterion. There may be other ways of meeting the criterion not covered by these techniques. 
+  that the Accessibility Guidelines Working Group deems sufficient for meeting this success criterion.
+  A technique may go beyond the minimum requirement of the criterion. There may be other ways of meeting the criterion not covered by these techniques.
   For information on using other techniques, see
   <a href="understanding-techniques">Understanding Techniques for WCAG Success Criteria</a>,
   particularly the "Other Techniques" section.

_includes/understanding/techniques.html

@@ -7,8 +7,8 @@
   <h2>Techniques</h2>
   <p>
     Each numbered item in this section represents a technique or combination of techniques
-    that the Accessibility Guidelines Working Group deems sufficient for meeting this Success Criterion.
-    A technique may go beyond the minimum requirement of the criterion. There may be other ways of meeting the criterion not covered by these techniques. 
+    that the Accessibility Guidelines Working Group deems sufficient for meeting this success criterion.
+    A technique may go beyond the minimum requirement of the criterion. There may be other ways of meeting the criterion not covered by these techniques.
     For information on using other techniques, see
     <a href="understanding-techniques">Understanding Techniques for WCAG Success Criteria</a>,
     particularly the "Other Techniques" section.