ci: exclude cruft from code coverage

[Stebalien]

1. Exclude generated code.
2. Exclude generated actors, we mostly test against the latest version.

[Stebalien]

E.g., see https://app.codecov.io/gh/filecoin-project/lotus/compare/7187/changes. We're getting 31 lines from the v2 actors.

[codecov]

Codecov Report

Merging #7189 (1cecf3c) into master (8bcd917) will increase coverage by 4.24%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7189      +/-   ##
==========================================
+ Coverage   34.84%   39.08%   +4.24%     
==========================================
  Files         688      607      -81     
  Lines       80386    64565   -15821     
==========================================
- Hits        28013    25238    -2775     
+ Misses      46672    34946   -11726     
+ Partials     5701     4381    -1320     

Impacted Files	Coverage Δ
api/client/client.go	38.98% <0.00%> (-7.60%)	⬇️
chain/actors/builtin/paych/paych.go	16.88% <0.00%> (-5.20%)	⬇️
storage/wdpost_sched.go	77.22% <0.00%> (-3.97%)	⬇️
node/hello/hello.go	63.21% <0.00%> (-3.45%)	⬇️
chain/store/store.go	63.41% <0.00%> (-1.07%)	⬇️
extern/sector-storage/sched_worker.go	77.97% <0.00%> (-0.73%)	⬇️
chain/sync_manager.go	66.77% <0.00%> (-0.63%)	⬇️
cmd/tvx/stores.go	0.00% <0.00%> (ø)
storage/wdpost_changehandler.go	98.11% <0.00%> (ø)
extern/sector-storage/stores/local.go	59.25% <0.00%> (ø)
... and 92 more

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