fix(.github): links in PR template (#4905)

fix(.github): PR template links

The links don't work when viewing the markdown file but do when viewed in PRs.

Signed-off-by: Mike Beaumont <mjboamail@gmail.com>

.github/PULL_REQUEST_TEMPLATE.md

@@ -15,8 +15,8 @@ If something doesn't apply please check the box and add a justification after th
 - [ ] E2E Tests --
 - [ ] Manual Universal Tests --
 - [ ] Manual Kubernetes Tests --
-- [ ] Do you need to update [`UPGRADE.md`](/UPGRADE.md)? --
-- [ ] Does it need to be backported according to the [backporting policy](/CONTRIBUTING.md#backporting)? --
-- [ ] Do you need to explicitly set a [`> Changelog:` entry here](/CONTRIBUTING.md#submitting-a-patch)?
+- [ ] Do you need to update [`UPGRADE.md`](../blob/master/UPGRADE.md)? --
+- [ ] Does it need to be backported according to the [backporting policy](../blob/master/CONTRIBUTING.md#backporting)? --
+- [ ] Do you need to explicitly set a [`> Changelog:` entry here](../blob/master/CONTRIBUTING.md#submitting-a-patch)?
 
 [1]: https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword