Rm array allocation in {en,dis}able_query_cache!

When `dirties` was [added][1] as an option to `uncached`,
`{en,dis}able_query_cache!` were changed to use multiple assignment.
However, multiple assignment allocates an array and is not really
necessary for these methods.

[1]: 5d528ba

Surprisingly, this showed up in a production profile as a large
allocator.

Reproduction:

```ruby
require "active_record"
require "memory_profiler"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")

report = MemoryProfiler.report do
  10000.times do
    ActiveRecord::Base.connection.enable_query_cache!
  end
end

report.pretty_print
```

Before:

```
bundle exec ruby eqc.rb | rg "allocated objects by class" -A 10
allocated objects by class
-----------------------------------
     10093  Array
      1551  String
        12  Class
         7  Hash
         3  File
         2  Proc
         2  Thread::Backtrace
         2  Thread::Backtrace::Location
         2  Thread::Mutex
```

After:

```
bundle exec ruby eqc.rb | rg "allocated objects by class" -A 10
allocated objects by class
-----------------------------------
      1551  String
        93  Array
        12  Class
         7  Hash
         3  File
         2  Proc
         2  Thread::Backtrace
         2  Thread::Backtrace::Location
         2  Thread::Mutex
```

Author: skipkayhil

activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb

@@ -157,11 +157,13 @@ def enable_query_cache
         end
 
         def enable_query_cache!
-          query_cache.enabled, query_cache.dirties = true, true
+          query_cache.enabled = true
+          query_cache.dirties = true
         end
 
         def disable_query_cache!
-          query_cache.enabled, query_cache.dirties = false, true
+          query_cache.enabled = false
+          query_cache.dirties = true
         end
 
         def query_cache_enabled