tests: set developer in ENV rather than stubbing

Library/Homebrew/test/audit_test.rb

@@ -243,7 +243,7 @@ class FormulaAuditorTests < Homebrew::TestCase
     needs_compat
     require "compat/formula_specialties"
 
-    ARGV.stubs(:homebrew_developer?).returns false
+    ENV.delete("HOMEBREW_DEVELOPER")
     fa = shutup do
       formula_auditor "foo", <<-EOS.undent
         class Foo < GithubGistFormula
@@ -260,7 +260,7 @@ class FormulaAuditorTests < Homebrew::TestCase
     needs_compat
     require "compat/formula_specialties"
 
-    ARGV.stubs(:homebrew_developer?).returns false
+    ENV.delete("HOMEBREW_DEVELOPER")
     fa = formula_auditor "foo", <<-EOS.undent
       class Foo < ScriptFileFormula
         url "http://example.com/foo-1.0.tgz"
@@ -275,7 +275,7 @@ class FormulaAuditorTests < Homebrew::TestCase
     needs_compat
     require "compat/formula_specialties"
 
-    ARGV.stubs(:homebrew_developer?).returns false
+    ENV.delete("HOMEBREW_DEVELOPER")
     fa = formula_auditor "foo", <<-EOS.undent
       class Foo < AmazonWebServicesFormula
         url "http://example.com/foo-1.0.tgz"

Library/Homebrew/test/os/mac/diagnostic_test.rb

@@ -16,7 +16,7 @@ class OSMacDiagnosticChecksTest < Homebrew::TestCase
   end
 
   def test_check_for_unsupported_macos
-    ARGV.stubs(:homebrew_developer?).returns false
+    ENV.delete("HOMEBREW_DEVELOPER")
     OS::Mac.stubs(:prerelease?).returns true
     assert_match "We do not provide support for this pre-release version.",
       @checks.check_for_unsupported_macos

Library/Homebrew/test/utils_test.rb

@@ -207,7 +207,7 @@ class UtilTests < Homebrew::TestCase
   end
 
   def test_odeprecated
-    ARGV.stubs(:homebrew_developer?).returns false
+    ENV.delete("HOMEBREW_DEVELOPER")
     e = assert_raises(MethodDeprecatedError) do
       odeprecated("method", "replacement",
         caller: ["#{HOMEBREW_LIBRARY}/Taps/homebrew/homebrew-core/"],