fix: Don't throw for unknown network option

[spypsy]

We are currently failing on next-net deployments with:

Failed to fetch network config for network: next-net

When a network that's not part of our config is used, we shouldn't throw if the fetch is successful. Instead we just don't hydrate any env and keep going.

[AztecBot]

Flakey Tests

🤖 says: This CI run detected 1 tests that failed, but were tolerated due to a .test_patterns.yml entry.

\033FLAKED\033 (\0338;;http://ci.aztec-labs.com/afedf703901d5a2aafedf703901d5a2a8;;\033): yarn-project/end-to-end/scripts/run_test.sh simple src/e2e_p2p/inactivity_slash.test.ts (360s) (code: 1) group:e2e-p2p-epoch-flakes (\033Aztec Bot\033: fix: Don't throw for unknown network option (#18585))

[AztecBot]

❌ Failed to cherry-pick to v2 due to conflicts. Please backport manually.