tests: adjust header-links sample set to use parenthesis

Adjusting the header-links sample set to use parenthesis for rst
documents to help sanity check odd Confluence Cloud anchor scenarios.

Signed-off-by: James Knight <git@jdknight.me>

Author: jdknight

tests/sample-sets/header-links/rst-v1-first.rst

@@ -66,8 +66,8 @@ Vivamus iaculis, sapien ac blandit faucibus, mauris felis sodales enim, et facil
 
 .. _main-rst-v1-extra2:
 
-An Extra Header
----------------
+An (Extra) Header
+-----------------
 
 .. note::
 

tests/sample-sets/header-links/rst-v2-first.rst

@@ -66,8 +66,8 @@ Vivamus iaculis, sapien ac blandit faucibus, mauris felis sodales enim, et facil
 
 .. _main-rst-v2-extra2:
 
-An Extra Header
----------------
+An (Extra) Header
+-----------------
 
 .. note::