ci/lint: add integration tag

In the current PRs we have an issue with the linter failing on a dead code
in integration tests. The linter isn't failing on main_test.go file
because it somehow ignores the integration tag. However, it fails on
other files which main_test.go depends on and which have the integration
tag.

This commit tells golangci-lint to always use the integration tag while doing
the inspection.

.golangci.yml

@@ -4,6 +4,10 @@ linters-settings:
       - shadow # default value recommended by golangci
       - composites
 
+run:
+  build-tags:
+    - integration
+
 issues:
   # Maximum issues count per one linter. Set to 0 to disable. Default is 50.
   max-issues-per-linter: 0