fix(x/ecocredit): fix create class fee if not required and update tests

[ryanchristo]

Description

Ref: #893

---

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[codecov]

Codecov Report

Merging #1234 (7d599ad) into master (eb783ea) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1234      +/-   ##
==========================================
- Coverage   80.05%   80.02%   -0.03%     
==========================================
  Files         232      231       -1     
  Lines       21495    21433      -62     
==========================================
- Hits        17208    17152      -56     
- Misses       2968     2980      +12     
+ Partials     1319     1301      -18     

Flag	Coverage Δ
experimental-codecov	80.02% <100.00%> (-0.08%)	⬇️
stable-codecov	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
x/ecocredit/server/basket/msg_create.go	90.29% <100.00%> (+1.52%)	⬆️
x/ecocredit/server/core/msg_create_class.go	79.16% <100.00%> (ø)
x/ecocredit/server/utils/test_utils.go	0.00% <0.00%> (-100.00%)	⬇️
types/ormstore/store.go	33.55% <0.00%> (-6.19%)	⬇️
types/coin.go	59.79% <0.00%> (-0.77%)	⬇️
app/stable_appconfig.go

[technicallyty]

might be nice to have the balance in the error