Conform to code review.

Only enable Explorer.ExchangeRates when it's needed.
Also changed the required store based on the app needed.
IE: BlockScoutWeb tests didn't care about the store but Explorer tests did.

apps/block_scout_web/config/test.exs

@@ -17,3 +17,5 @@ config :logger, :block_scout_web,
 
 # Configure wallaby
 config :wallaby, screenshot_on_failure: true
+
+config :explorer, Explorer.ExchangeRates, enabled: false, store: :none

apps/explorer/config/test.exs

@@ -15,7 +15,7 @@ config :explorer, Explorer.Repo,
   pool_timeout: 10_000,
   ownership_timeout: 60_000
 
-config :explorer, Explorer.ExchangeRates, enabled: true
+config :explorer, Explorer.ExchangeRates, enabled: false, store: :ets
 
 config :explorer, Explorer.Market.History.Cataloger, enabled: false
 

config/test.exs

@@ -12,4 +12,4 @@ config :logger, :error, path: Path.absname("logs/test/error.log")
 
 config :explorer, Explorer.ExchangeRates,
   source: Explorer.ExchangeRates.Source.NoOpSource,
-  store: :ets
+  store: :none