Update Github workflows for the 6.x branch (#646)

Author: jasonhebert

.github/workflows/automation-changelog-update.yml

@@ -3,7 +3,7 @@ name: "Automation - Changelog Update"
 on:
   push:
     branches:
-      - "4.x"
+      - "6.x"
 
 jobs:
   automation:

.github/workflows/docs.yml

@@ -4,8 +4,7 @@ on:
   pull_request:
   push:
     branches:
-      - "3.x"
-      - "4.x"
+      - "6.x"
 
 jobs:
   documentation-linter:

README.md

@@ -61,7 +61,7 @@ This library is not in a stable stage yet, please use with caution.
 | [2.x](https://github.com/amazon-php/sp-api-sdk/tree/2.x) | 🚫         |
 | [3.x](https://github.com/amazon-php/sp-api-sdk/tree/3.x) | 🚫         |
 | [4.x](https://github.com/amazon-php/sp-api-sdk/tree/4.x) | 🚫         |
-| [5.x](https://github.com/amazon-php/sp-api-sdk/tree/5.x) | ✅         |
+| [5.x](https://github.com/amazon-php/sp-api-sdk/tree/5.x) | 🚫         |
 | [6.x](https://github.com/amazon-php/sp-api-sdk/tree/6.x) | ✅         |
 
 Version <s> [1.x](https://github.com/amazon-php/sp-api-sdk/tree/1.x) </s> is deprecated becuase of the attempt to