[CI] Exclude tests that call external APIs

[t-bast]

These tests have been flaky because external APIs tend to be down or throttle our calls. and we don't want our test suite to fail because of that.

In practice it's enough if developers run these tests locally once in a while.

[pm47]

Nice trick

[t-bast]

😎

[codecov-io]

Codecov Report

Merging #1622 (d069af7) into master (8bfb9f0) will decrease coverage by 0.55%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1622      +/-   ##
==========================================
- Coverage   87.25%   86.70%   -0.56%     
==========================================
  Files         146      146              
  Lines       11063    11063              
  Branches      503      503              
==========================================
- Hits         9653     9592      -61     
- Misses       1410     1471      +61     

Impacted Files	Coverage Δ
...acinq/eclair/blockchain/watchdogs/Monitoring.scala	0.00% <0.00%> (-100.00%)	⬇️
...q/eclair/blockchain/watchdogs/HeadersOverDns.scala	16.66% <0.00%> (-60.42%)	⬇️
...acinq/eclair/blockchain/fee/BitgoFeeProvider.scala	58.33% <0.00%> (-37.51%)	⬇️
...lair/blockchain/watchdogs/BlockchainWatchdog.scala	60.00% <0.00%> (-35.00%)	⬇️
...cinq/eclair/blockchain/watchdogs/ExplorerApi.scala	54.28% <0.00%> (-34.29%)	⬇️
.../eclair/blockchain/fee/EarnDotComFeeProvider.scala	70.37% <0.00%> (-29.63%)	⬇️
...clair/blockchain/electrum/ElectrumClientPool.scala	78.49% <0.00%> (-1.08%)	⬇️
...nq/eclair/blockchain/electrum/ElectrumClient.scala	73.52% <0.00%> (+0.36%)	⬆️
...q/eclair/blockchain/electrum/ElectrumWatcher.scala	77.77% <0.00%> (+0.79%)	⬆️
...main/scala/fr/acinq/eclair/router/Validation.scala	92.91% <0.00%> (+1.49%)	⬆️
... and 1 more