fix DHIS2 exporter spec ordering bug (#5305)

The DHIS2 exporter specs (BD and ET) don't play well with each other.
For one, fetching the data elements file is a memoized call, which
causes the tests to break if they are both running in the same process,
because the file that was loaded first is always returned, regardless of
the actual change in the `DHIS2_DATA_ELEMENTS_FILE` envvar. This
probably went undetected for a while because the two specs ended up
running in different test runners most of the time.

This enmity between the specs runs deeper, though. It turns out that our
mock in the Ethiopia exporter spec does not protect us from a method
call to `Dhis2.client`. When the Ethiopia exporter spec is run first,
it's not an issue, because the `Dhis2` gem creates an empty
configuration object, and the call to the `:client` method will assume
an uncredentialed server and work fine.

But when the Bangladesh exporter spec is run first, it configures the
`Dhis2` gem with an empty username-password combination. This value is
_cached_. So when we get to the Ethiopia spec, where our client is
mocked, the method invocation causes it to build a URI with an empty
username-password combination which causes the underlying URI parsing
library to throw an exception.

The fix for the latter is to make the client itself a double and not get
into the hairy details of the `Dhis2` gem caching behaviour. May the
specs live in harmony again.

config/initializers/country_config.rb

@@ -83,9 +83,7 @@ class CountryConfig
   }.with_indifferent_access.freeze
 
   class << self
-    include Memery
-
-    memoize def dhis2_data_elements
+    def dhis2_data_elements
       YAML.load_file(ENV.fetch("DHIS2_DATA_ELEMENTS_FILE")).with_indifferent_access
     end
   end

spec/exporters/dhis2/ethiopia_exporter_spec.rb

@@ -50,7 +50,9 @@
       end
 
       data_value_sets = double
-      allow(Dhis2.client).to receive(:data_value_sets).and_return(data_value_sets)
+      dhis2_client = double
+      allow(Dhis2).to receive(:client).and_return(dhis2_client)
+      allow(dhis2_client).to receive(:data_value_sets).and_return(data_value_sets)
       expect(data_value_sets).to receive(:bulk_create).with(data_values: expected_values[0])
       expect(data_value_sets).to receive(:bulk_create).with(data_values: expected_values[1])
       Dhis2::EthiopiaExporter.export