Revert "staging_with_rekorv2 uses embedded trust config"

This reverts commit d7ddd50.

Author: ramonpetgrave64

test/unit/conftest.py

@@ -31,6 +31,7 @@
 from id import (
     detect_credential,
 )
+from sigstore_protobuf_specs.dev.sigstore.trustroot.v1 import Service
 from tuf.api.exceptions import DownloadHTTPError
 from tuf.ngclient import FetcherInterface, updater
 
@@ -238,20 +239,19 @@ def signer():
 
 
 @pytest.fixture
-def staging_with_rekorv2(
-    asset,
-) -> tuple[type[SigningContext], type[Verifier], IdentityToken]:
+def staging_with_rekorv2() -> tuple[
+    type[SigningContext], type[Verifier], IdentityToken
+]:
     """
     Returns a SigningContext, Verifier, and IdentityToken for the staging environment.
     The signingContext will use the Rekor V2 instance even if it is not yet enabled in
     staging signing config.
     """
 
     def signer():
-        trust_config = ClientTrustConfig.from_json(
-            asset(
-                os.path.join("trust_config", "staging-but-sign-with-rekor-v2.json")
-            ).read_text()
+        trust_config = ClientTrustConfig.staging()
+        trust_config.signing_config._tlogs.append(
+            Service("https://log2025-alpha1.rekor.sigstage.dev", 2)
         )
         return SigningContext.from_trust_config(trust_config)