Set/Override config.default_funder_name for tests

The 'User creates a new Plan' test will not pass unless an org exists within the db such that  `org.name == Rails.application.config.default_funder_name`. However, we have `config.default_funder_name = Rails.application.secrets.default_funder_name` within `config/application.rb`. This secret is not read while executing the tests via our GitHub actions and the following error is encountered:

```
  1) Plans User creates a new Plan
     Failure/Error: @funding_org  = create(:org, :funder, templates: 1, name: Rails.application.config.default_funder_name)

     ActiveRecord::RecordInvalid:
       Validation failed: Name can't be blank
     # ./spec/features/plans_spec.rb:13:in `block (2 levels) in <top (required)>'
```

 Thus, we are overriding/setting that value within the test itself.

Author: aaronskiba

spec/features/plans_spec.rb

@@ -10,6 +10,7 @@
     @org = create(:org)
     @research_org = create(:org, :organisation, :research_institute,
                            name: 'Test Research Org', templates: 1)
+    Rails.application.config.default_funder_name = 'Test Funder'
     @funding_org  = create(:org, :funder, templates: 1, name: Rails.application.config.default_funder_name)
     @template     = create(:template, org: @org)
     @user         = create(:user, org: @org)