feedback: Fix sys_info header contrast.

Previously, the background of the header was too light for the text that
it contained. With this change, the ratio is now 4.5.

BUG=chromium:1005543
TEST=Verified contrast of a screenshot with color contrast checker.

Change-Id: Ia3b67419ee4b69181afb6e0084c593d13b00ec05
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1887727Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Miriam Zimmerman <mutexlox@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710595}

chrome/browser/resources/about_sys/about_sys.css

@@ -39,7 +39,7 @@ h2 {
 }
 
 #header {
-  background: rgb(82, 150, 222);
+  background: rgb(60, 111, 235);
   background-size: 100%;
   border: 1px solid rgb(58, 117, 189);
   border-radius: 6px;