sr/dt: default mode_mutability to true, matching the broker

The broker-side default, defined in
src/v/pandaproxy/schema_registry/configuration.cc, flipped to true in
0744a21
but the ducktape SchemaRegistryConfig stayed false. Align the harness
with the product default and drop the now-redundant per-test true
overrides, except in the ModeMutable test classes, which pin the flag
they exercise (mirroring the explicit false in ModeNotMutableTest).

Author: pgellert

tests/rptest/services/redpanda.py

@@ -1277,7 +1277,7 @@ class SchemaRegistryConfig(TlsConfig):
     SR_TLS_CLIENT_KEY_FILE = "/etc/redpanda/sr_client.key"
     SR_TLS_CLIENT_CRT_FILE = "/etc/redpanda/sr_client.crt"
 
-    mode_mutability = False
+    mode_mutability = True
 
     def __init__(self) -> None:
         super(SchemaRegistryConfig, self).__init__()

tests/rptest/tests/audit_log_test.py

@@ -3000,7 +3000,6 @@ class AuditLogTestSchemaRegistryBase(AuditLogTestBase):
     def __init__(self, test_context, **kwargs):
         sr_config = SchemaRegistryConfig()
         sr_config.authn_method = "http_basic"
-        sr_config.mode_mutability = True
         extra_rp_conf = {"schema_registry_use_rpc": False}
         if "extra_rp_conf" in kwargs:
             extra_rp_conf.update(kwargs.pop("extra_rp_conf"))

tests/rptest/tests/rpk_registry_test.py

@@ -71,7 +71,6 @@ def __init__(self, ctx, schema_registry_config=SchemaRegistryConfig()):
 
         self.schema_registry_config = SchemaRegistryConfig()
         self.schema_registry_config.require_client_auth = True
-        self.schema_registry_config.mode_mutability = True
 
     # Override Redpanda start to create the certs and enable auth.
     def setUp(self):

tests/rptest/tests/schema_registry_test.py

@@ -5208,14 +5208,11 @@ class SchemaRegistryContextTestBase(SchemaRegistryEndpoints):
     """
 
     def __init__(self, context: TestContext, **kwargs: Any):
-        schema_registry_config = SchemaRegistryConfig()
-        schema_registry_config.mode_mutability = True
         extra_rp_conf = {}
         if "extra_rp_conf" in kwargs:
             extra_rp_conf.update(kwargs.pop("extra_rp_conf"))
         super().__init__(
             context,
-            schema_registry_config=schema_registry_config,
             extra_rp_conf=extra_rp_conf,
             **kwargs,
         )
@@ -7379,7 +7376,6 @@ def __init__(self, context, **kwargs):
 
         schema_registry_config = SchemaRegistryConfig()
         schema_registry_config.authn_method = "http_basic"
-        schema_registry_config.mode_mutability = True
 
         extra_rp_conf = {}
         if "extra_rp_conf" in kwargs:
@@ -10472,7 +10468,6 @@ def __init__(self, context, extra_rp_conf: dict | None = None, **kwargs):
 
         schema_registry_config = SchemaRegistryConfig()
         schema_registry_config.authn_method = "http_basic"
-        schema_registry_config.mode_mutability = True
 
         merged_rp_conf = {"schema_registry_use_rpc": False}
         if extra_rp_conf: