fix(rpc): nextBaseFee for fee history (backport: #1720)

[mmsqe]

for more info: evmos#1720

Description

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

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[codecov]

Codecov Report

Merging #234 (cc25207) into release/v0.20.x-cronos (cb741e1) will decrease coverage by 0.40%.
The diff coverage is 0.00%.

@@                    Coverage Diff                     @@
##           release/v0.20.x-cronos     #234      +/-   ##
==========================================================
- Coverage                   57.20%   56.81%   -0.40%     
==========================================================
  Files                         108      108              
  Lines                       10149    10220      +71     
==========================================================
  Hits                         5806     5806              
- Misses                       4096     4167      +71     
  Partials                      247      247              

Impacted Files	Coverage Δ
rpc/backend/chain_info.go	8.99% <0.00%> (-1.13%)	⬇️
rpc/backend/utils.go	6.60% <0.00%> (-1.87%)	⬇️