Makefile: Pass PAGER/GIT_PAGER variable

Allow to override the PAGER/GIT_PAGER variables inside the container.
Use `cat` as pager when running in Github Actions (to avoid things like
`git diff` stalling the CI).

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

.github/workflows/test.yml

@@ -14,6 +14,8 @@ on:
 
 env:
   GO_VERSION: "1.21.7"
+  GIT_PAGER: "cat"
+  PAGER: "cat"
 
 jobs:
   validate-dco: