Update old wiki links (#149544)

Part of https://github.com/flutter/flutter/issues/145009

Finishes updating links in the repo that pointed to the old wiki

.github/ISSUE_TEMPLATE/7_cherry_pick.yml

@@ -38,7 +38,7 @@ body:
       label: Changelog Description
       description: >-
         Explain this CP in less than 80 characters that is accessible to most Flutter developers
-        See https://github.com/flutter/flutter/wiki/Hotfix-Documentation-Best-Practices for examples
+        See https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md for examples
     validations:
       required: true
   - type: input

.github/ISSUE_TEMPLATE/8_design_doc.yml

@@ -8,7 +8,7 @@ body:
         Thank you for your interest in contributing to Flutter!
 
         Please ensure that you are following
-        https://github.com/flutter/flutter/wiki/Design-Documents
+        https://github.com/flutter/flutter/blob/main/docs/contributing/Design-Documents.md
         when sharing a design document.
 
         Please fill out the sections below to the best of your ability.