Move dtos devops template repo to main (#386)

# What is the change?

Updating the dtos-devops-template so its pointing to the main branch.
Please note that the PR to update the dtos-devops-template to add the
additional steps so the AVD works has already been done. Below is
evidence that it works using the main branch: -


https://dev.azure.com/nhse-dtos/lung-cancer-screening/_build/results?buildId=35903&view=logs&j=c970d263-77bb-52d7-1861-5b2637d7126d&t=c970d263-77bb-52d7-1861-5b2637d7126d

<!-- Describe the intended changes. -->

# Why are we making this change?

<!-- Why is this change required? What problem does it solve? -->

Author: mrlockstar

.azuredevops/pipelines/hub-infrastructure-dev.yaml

@@ -11,7 +11,7 @@ resources:
     - repository: dtos-devops-templates
       type: github
       name: NHSDigital/dtos-devops-templates
-      ref: PPHA-417-Create-infra-as-code-for-Hub-resources
+      ref: main
       endpoint: NHSDigital
 
 variables:

.azuredevops/pipelines/hub-infrastructure-live.yaml

@@ -11,7 +11,7 @@ resources:
     - repository: dtos-devops-templates
       type: github
       name: NHSDigital/dtos-devops-templates
-      ref: PPHA-417-Create-infra-as-code-for-Hub-resources
+      ref: main
       endpoint: NHSDigital
 
 variables: