ci: Add codecov.yaml to silence red-herring errors

[alexec]

Copied verbatim from Argo CD

[codecov]

Codecov Report

Merging #5482 (0a83873) into master (5bd7ce8) will increase coverage by 30.16%.
The diff coverage is n/a.

❗ Current head 0a83873 differs from pull request most recent head 5ce591c. Consider uploading reports for the commit 5ce591c to get more accurate results

@@             Coverage Diff             @@
##           master    #5482       +/-   ##
===========================================
+ Coverage   16.50%   46.66%   +30.16%     
===========================================
  Files         243      240        -3     
  Lines       43774    14982    -28792     
===========================================
- Hits         7225     6992      -233     
+ Misses      35568     7092    -28476     
+ Partials      981      898       -83     

Impacted Files	Coverage Δ
pkg/apiclient/http1-client.go	0.00% <0.00%> (ø)
pkg/apiclient/logs-intermediary.go	0.00% <0.00%> (ø)
...piclient/argo-kube-cron-workflow-service-client.go	0.00% <0.00%> (ø)
pkg/apis/workflow/v1alpha1/generated.pb.go
...kg/apis/workflow/v1alpha1/zz_generated.deepcopy.go
pkg/apis/workflow/v1alpha1/openapi_generated.go
pkg/apiclient/apiclient.go	10.00% <0.00%> (+4.44%)	⬆️

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[alexec]

functional_test.go:530: timeout after 30s waiting for condition