Update codecov github action

[mcpherrinm]

Update codecov action to v3

The v1 action is deprecated, as is the underlying bash script it uses.

[codecov]

Codecov Report

Merging #395 (de5c87d) into master (de5bd1e) will decrease coverage by 5.29%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #395      +/-   ##
==========================================
- Coverage   83.73%   78.45%   -5.29%     
==========================================
  Files          25       30       +5     
  Lines        1113     2130    +1017     
==========================================
+ Hits          932     1671     +739     
- Misses        131      379     +248     
- Partials       50       80      +30     

Flag	Coverage Δ
darwin	77.42% <ø> (?)
linux	83.48% <ø> (-0.26%)	⬇️

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

Impacted Files	Coverage Δ
socket/net.go	90.00% <0.00%> (-1.49%)	⬇️
certloader/spiffe_tls_config.go	81.66% <0.00%> (-0.69%)	⬇️
certloader/certtlsconfig.go	85.36% <0.00%> (-0.35%)	⬇️
status.go	96.51% <0.00%> (-0.16%)	⬇️
doc.go	100.00% <0.00%> (ø)
unix.go	100.00% <0.00%> (ø)
signals.go	100.00% <0.00%> (ø)
policy/wrap.go	100.00% <0.00%> (ø)
policy/loader.go	100.00% <0.00%> (ø)
certloader/dialer.go	100.00% <0.00%> (ø)
... and 20 more

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