Updated the .lintr configuration to match with that in packagetemplate

.lintr

@@ -7,6 +7,10 @@ linters: linters_with_tags(
     todo_comment_linter = NULL,
     function_argument_linter = NULL,
     cyclocomp_linter = NULL,
-    # Use minimum R declared in DESCRIPTION or fall back to current R version
+    # Use minimum R declared in DESCRIPTION or fall back to current R version.
+    # Install etdev package from https://github.com/epiverse-trace/etdev
     backport_linter(if (length(x <- etdev::extract_min_r_version())) x else getRversion())
-    )
+  )
+exclusions: list(
+    "tests/testthat.R" = list(unused_import_linter = Inf)
+  )