Fix broken formatting in http repository rules documentation page.

Fixes https://github.com/bazelbuild/bazel/issues/10990

RELNOTES:
PiperOrigin-RevId: 302550934
diff --git a/tools/build_defs/repo/http.bzl b/tools/build_defs/repo/http.bzl
index 04efba8..1a57b44 100644
--- a/tools/build_defs/repo/http.bzl
+++ b/tools/build_defs/repo/http.bzl
@@ -218,6 +218,7 @@
         "storage.cloudprovider.com": "Bearer <password>"
     }
 )
+```
 
 netrc: