Bump RuboCop to 0.67.2

Performance cops will be extracted from RuboCop to RuboCop Performance
when next RuboCop 0.68 will be released.
https://github.com/rubocop-hq/rubocop/issues/5977

RuboCop 0.67 is its transition period.

Since rails/rails repository uses Performance cops, This PR added
rubocop-performance gem to Gemfile.

And this PR fixes some offenses using the following auto-correct.

```console
% bundle exec rubocop -a

Offenses:

activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb:212:26:
C: [Corrected] Layout/SpaceAroundOperators: Operator =
> should be surrounded by a single space.
              "primary"  => { adapter: "sqlite3", database: "db/primary.sqlite3" }
                         ^^
activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb:239:26:
C: [Corrected] Layout/SpaceAroundOperators: Operator => should be
surrounded by a single space.
              "primary"  => { adapter: "sqlite3", database: "db/primary.sqlite3" }
                         ^^
actionview/test/template/resolver_shared_tests.rb:1:1: C: [Corrected]
Style/FrozenStringLiteralComment: Missing magic comment #
frozen_string_literal: true.
module ResolverSharedTests
^
actionview/test/template/resolver_shared_tests.rb:10:33: C: [Corrected]
Layout/SpaceAroundEqualsInParameterDefault: Surrounding space missing in
default value assignment.
  def with_file(filename, source="File at #{filename}")
                                ^
actionview/test/template/resolver_shared_tests.rb:106:5: C: [Corrected]
Rails/RefuteMethods: Prefer assert_not_same over refute_same.
    refute_same a, b
    ^^^^^^^^^^^

2760 files inspected, 5 offenses detected, 5 offenses corrected
```

1 files changed, 4 insertions, 2 deletions

diff --git a/actionview/test/template/resolver_shared_tests.rb b/actionview/test/template/resolver_shared_tests.rb
index 525b452075..8b47c5bc89 100644
--- a/actionview/test/template/resolver_shared_tests.rb
+++ b/actionview/test/template/resolver_shared_tests.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ResolverSharedTests
   attr_reader :tmpdir
 
@@ -7,7 +9,7 @@ module ResolverSharedTests
     end
   end
 
-  def with_file(filename, source="File at #{filename}")
+  def with_file(filename, source = "File at #{filename}")
     path = File.join(tmpdir, filename)
     FileUtils.mkdir_p(File.dirname(path))
     File.write(path, source)
@@ -103,7 +105,7 @@ module ResolverSharedTests
     c = context.find("hello_world", "test", false, [], {})
 
     # disable_cache should give us a new object
-    refute_same a, b
+    assert_not_same a, b
 
     # but it should not clear the cache
     assert_same a, c