Rails 6: Coerce ReloadModelsTest test on Windows

[aidanharan]

The ReloadModelsTest#test_has_one_with_reload test fails on Windows because too many arguments are being passed to create the new subprocess (https://github.com/rails/rails/blob/v6.0.3/activesupport/lib/active_support/testing/isolation.rb#L93).

On the AppVeyor CI, when all tests are being run the test is calling IO.popen with 442 arguments (see https://ci.appveyor.com/project/wpolicarpo/activerecord-sqlserver-adapter/builds/32821521/job/e47ljgrcbpmmiuyf). Because of the number of arguments or the total length of the arguments a Arg list too long - C:/Ruby25-x64/bin/ruby.exe (Errno::E2BIG) exception is being thrown.

Variable	Number of arguments
load_path_args	166
$0	1
ORIG_ARGV	274
test_opts	1

If just the ReloadModelsTest#test_has_one_with_reload is run then the number of arguments in ORIG_ARGV is reduced to 2 and the test passes. See https://ci.appveyor.com/project/wpolicarpo/activerecord-sqlserver-adapter/builds/32821146/job/nr3abuyi476eu0s7

Coercing the ReloadModelsTest#test_has_one_with_reload test if being run on a Windows environment.