fix: pinning nim-eth dependency

[AuHau]

Pins nim-eth to a working version.

Fixes compilation errors with nim v2.2.0.

First compilation error was a symbol clash for fromJson:

/home/runner/.nimble/pkgs2/serde-1.2.1-3596e180893eb8035d42cd1d778d2eff8f8fca25/serde/json/deserializer.nim(163, 19) Error: ambiguous call; both deserializer.fromJson(T: typedesc[enum], json: JsonNode) [proc declared in /home/runner/.nimble/pkgs2/serde-1.2.1-3596e180893eb8035d42cd1d778d2eff8f8fca25/serde/json/deserializer.nim(54, 6)] and conversions.fromJson(T: typedesc[E: TransactionStatus or TransactionType], json: JsonNode) [proc declared in /home/runner/work/nim-ethers/nim-ethers/ethers/providers/jsonrpc/conversions.nim(97, 6)] match for: (typedesc[TransactionType], JsonNode)

Second error was another ambiguous symbol for fail inside the tests.

[emizzle]

Pinning nim-eth is a temporary fix until proper versioning is implemented.