tests: remove linkage cache env.

Otherwise this will mess with `brew tests`.

Library/Homebrew/dev-cmd/tests.rb

@@ -38,6 +38,7 @@ module Homebrew
       ENV.delete("VERBOSE")
       ENV.delete("HOMEBREW_CASK_OPTS")
       ENV.delete("HOMEBREW_TEMP")
+      ENV.delete("HOMEBREW_LINKAGE_CACHE")
       ENV["HOMEBREW_NO_ANALYTICS_THIS_RUN"] = "1"
       ENV["HOMEBREW_DEVELOPER"] = "1"
       ENV["HOMEBREW_NO_COMPAT"] = "1" if args.no_compat?

Library/Homebrew/test/spec_helper.rb

@@ -43,8 +43,8 @@ RSpec.configure do |config|
 
   config.filter_run_when_matching :focus
 
-  # TODO when https://github.com/rspec/rspec-expectations/pull/1056 makes
-  # it into a stable release:
+  # TODO: when https://github.com/rspec/rspec-expectations/pull/1056
+  #       makes it into a stable release:
   # config.expect_with :rspec do |c|
   #   c.max_formatted_output_length = 200
   # end