fix: nightly tests (#595)

.github/tests/blobber.yaml

@@ -11,8 +11,6 @@ participants:
     el_image: ethpandaops/geth:master
     cl_type: lodestar
     count: 1
-network_params:
-  deneb_fork_epoch: 1
 additional_services:
   - dora
   - blob_spammer

.github/tests/ephemery.yaml

@@ -3,6 +3,7 @@ participants:
     cl_type: teku
   - el_type: nethermind
     cl_type: prysm
+    cl_image: gcr.io/prysmaticlabs/prysm/beacon-chain:stable
   - el_type: erigon
     cl_type: nimbus
   - el_type: besu
@@ -12,5 +13,5 @@ participants:
   - el_type: ethereumjs
     cl_type: teku
 network_params:
-  network: "ephemery"
+  network: ephemery
 additional_services: []

.github/tests/mix-with-deneb.yaml

-participants:
-  - el_type: geth
-    cl_type: teku
-  - el_type: nethermind
-    cl_type: prysm
-  - el_type: erigon
-    cl_type: nimbus
-  - el_type: besu
-    cl_type: lighthouse
-  - el_type: reth
-    cl_type: lodestar
-  - el_type: ethereumjs
-    cl_type: teku
-network_params:
-  deneb_fork_epoch: 1
-additional_services: []