Add tenv linter (open-telemetry#5524)

This starts adding more linters we aren't currently using, based on the
ones used by [the
collector](https://github.com/open-telemetry/opentelemetry-collector/blob/main/.golangci.yml#L122-L139).

This linter does not currently have any issues, so it requires no
further changes.
I'll be opening other PRs for linters that do require fixes.

* [tenv](https://github.com/sivchari/tenv) requires using `t.Setenv`
rather than `os.Setenv` in tests.

---------

Co-authored-by: Sam Xie <sam@samxie.me>

.golangci.yml

@@ -21,6 +21,7 @@ linters:
     - misspell
     - revive
     - staticcheck
+    - tenv
     - typecheck
     - unused