Use --primary-text-color in account dropdown

Follow-up to 43f3ba3.

Previously used header-text-color, but the dropdown background does not
use header-background-color. This may result in unexpected color
combinations with very low/no contrast.

Change-Id: Id38b9c22afbf3e970c53439b0c6020ee71685af5
diff --git a/polygerrit-ui/app/elements/core/gr-account-dropdown/gr-account-dropdown.html b/polygerrit-ui/app/elements/core/gr-account-dropdown/gr-account-dropdown.html
index bbe2877..d1ae719 100644
--- a/polygerrit-ui/app/elements/core/gr-account-dropdown/gr-account-dropdown.html
+++ b/polygerrit-ui/app/elements/core/gr-account-dropdown/gr-account-dropdown.html
@@ -31,7 +31,7 @@
           color: var(--header-text-color);
         }
         --gr-dropdown-item: {
-          color: var(--header-text-color);
+          color: var(--primary-text-color);
         }
       }
       gr-avatar {