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.

.github/workflows/local-testnet.yml

@@ -20,6 +20,9 @@ jobs:
           - ubuntu-22.04
           - macos-12
     runs-on: ${{ matrix.os }}
+    env:
+      # Enable portable to prevent issues with caching `blst` for the wrong CPU type
+      FEATURES: portable,jemalloc
     steps:
       - uses: actions/checkout@v3