ci: fix release notes template formatting.

[winder]

Summary

There were two issues with the new release template:

• missing forward slash in the diff URL.
• The triple-dash separator turned the changelog into a header, which was not intentional.

[codecov[bot]]

Codecov Report

Merging #148 (28ff75e) into master (442791a) will increase coverage by 5.12%. Report is 58 commits behind head on master. The diff coverage is 82.54%.

@@            Coverage Diff             @@
##           master     #148      +/-   ##
==========================================
+ Coverage   67.66%   72.78%   +5.12%     
==========================================
  Files          32       38       +6     
  Lines        1976     2789     +813     
==========================================
+ Hits         1337     2030     +693     
- Misses        570      649      +79     
- Partials       69      110      +41     

Files Changed	Coverage Δ
conduit/data/block_export_data.go	100.00% <ø> (+92.30%)	:arrow_up:
conduit/metrics/metrics.go	100.00% <ø> (ø)
conduit/pipeline/metadata.go	73.52% <ø> (+4.41%)	:arrow_up:
conduit/plugins/config.go	100.00% <ø> (ø)
conduit/plugins/importers/algod/metrics.go	100.00% <ø> (ø)
...gins/processors/filterprocessor/fields/searcher.go	77.50% <ø> (ø)
...ins/processors/filterprocessor/filter_processor.go	83.82% <ø> (+3.54%)	:arrow_up:
...plugins/processors/filterprocessor/gen/generate.go	34.28% <ø> (ø)
conduit/plugins/processors/noop/noop_processor.go	64.70% <ø> (+6.81%)	:arrow_up:
pkg/cli/internal/list/list.go	20.75% <ø> (ø)
... and 22 more

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