Fix typo in documentation navbar.

Additional fix for #9056.

RELNOTES:  None.
PiperOrigin-RevId: 261315062
diff --git a/site/_layouts/documentation.html b/site/_layouts/documentation.html
index 625e4de..0f8515e 100644
--- a/site/_layouts/documentation.html
+++ b/site/_layouts/documentation.html
@@ -11,7 +11,7 @@
 {%   assign major_version = "master" %}
 {%   assign minor_version = "master" %}
 {% else % }
-{%   assign minor_version = version_components[0] | plus:0 %}
+{%   assign major_version = version_components[0] | plus:0 %}
 {%   assign minor_version = version_components[1] | plus:0 %}
 {% endif %}