Enable BLS portable feature on all CI tests (#4868)

## Issue Addressed

Addresses the recent CI failures caused by caching `blst` for the wrong CPU type. 

## Proposed Changes

- Use `FEATURES: jemalloc,portable` when building Lighthouse & `lcli` in tests
- Add a new `TEST_FEATURES` and set to `portable` for all CI test jobs.
- Updated Makefiles to read the `TEST_FEATURES` environment variable, and default to none.

testing/ef_tests/Cargo.toml

@@ -9,6 +9,7 @@ edition = { workspace = true }
 ef_tests = []
 milagro = ["bls/milagro"]
 fake_crypto = ["bls/fake_crypto"]
+portable = ["beacon_chain/portable"]
 
 [dependencies]
 bls = { workspace = true }