Add missing type hints to tests. (#14687)

Adds type hints to tests.metrics and tests.crypto.

changelog.d/14687.misc

@@ -0,0 +1 @@
+Add missing type hints.

mypy.ini

@@ -36,7 +36,6 @@ exclude = (?x)
    |tests/api/test_ratelimiting.py
    |tests/app/test_openid_listener.py
    |tests/appservice/test_scheduler.py
-   |tests/crypto/test_keyring.py
    |tests/events/test_presence_router.py
    |tests/events/test_utils.py
    |tests/federation/test_federation_catch_up.py
@@ -90,13 +89,16 @@ disallow_untyped_defs = False
 [mypy-tests.config.*]
 disallow_untyped_defs = True
 
+[mypy-tests.crypto.*]
+disallow_untyped_defs = True
+
 [mypy-tests.federation.transport.test_client]
 disallow_untyped_defs = True
 
 [mypy-tests.handlers.*]
 disallow_untyped_defs = True
 
-[mypy-tests.metrics.test_background_process_metrics]
+[mypy-tests.metrics.*]
 disallow_untyped_defs = True
 
 [mypy-tests.push.test_bulk_push_rule_evaluator]

tests/crypto/test_event_signing.py

@@ -33,12 +33,12 @@
 
 
 class EventSigningTestCase(unittest.TestCase):
-    def setUp(self):
+    def setUp(self) -> None:
         self.signing_key: SigningKey = decode_signing_key_base64(
             KEY_ALG, KEY_VER, SIGNING_KEY_SEED
         )
 
-    def test_sign_minimal(self):
+    def test_sign_minimal(self) -> None:
         event_dict = {
             "event_id": "$0:domain",
             "origin": "domain",
@@ -69,7 +69,7 @@ def test_sign_minimal(self):
             "aIbygsSdLOFzvdDjww8zUVKCmI02eP9xtyJxc/cLiBA",
         )
 
-    def test_sign_message(self):
+    def test_sign_message(self) -> None:
         event_dict = {
             "content": {"body": "Here is the message content"},
             "event_id": "$0:domain",