content/static: add test id to unit header title

Change-Id: I9bc8b3bd9a04aedb3ab3330a8ea66b6544eddfb6
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/304510
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
diff --git a/content/static/html/helpers/_unit_header.tmpl b/content/static/html/helpers/_unit_header.tmpl
index 435168c..12a71f7 100644
--- a/content/static/html/helpers/_unit_header.tmpl
+++ b/content/static/html/helpers/_unit_header.tmpl
@@ -76,7 +76,7 @@
         <img height="72px" width="72px" class="UnitHeader-logo" src="/static/img/go-logo-blue.svg" alt="Go">
       </a>
     </div>
-    <h1>{{.Title}}</h1>
+    <h1 data-test-id="UnitHeader-title">{{.Title}}</h1>
     {{range .PageLabels}}
       <span class="UnitHeader-badge">{{.}}</span>
     {{end}}