.golangci: ignore tests for goconst, raise occurrence threshold

Test fixtures repeat strings (IPs, tags, hostnames, user/email
names) by their nature; extracting each into a named constant
adds indirection without adding clarity. Keep goconst strict on
production code, off on tests.

  ignore-tests: true       drop test-fixture noise entirely
  min-occurrences: 5       raise from default 3 to filter
                           "happens thrice" non-vocabulary cases
  min-len: 6               skip short literals like "set", "get",
                           "new" that read better at call sites