PYTHON-5040 Fix mypy typing errors in synchro.py and gen-certs.py

Use bare type: ignore in synchro.py so it suppresses whichever import
error mypy raises depending on whether unasync is installed.  Add
arg-type ignore in gen-certs.py for a cryptography stubs version skew.

Author: blink1073

test/certificates/gen-certs.py

@@ -77,7 +77,7 @@ def aki_from_ca(ca_cert: x509.Certificate) -> x509.AuthorityKeyIdentifier:
     # keyid form: SHA-1 hash of the CA's public key.  Required by Python 3.14 /
     # OpenSSL 3.x strict chain building.  macOS OCSP enforcement on the server
     # side is bypassed via --tlsAllowInvalidCertificates, so keyid form is safe.
-    return x509.AuthorityKeyIdentifier.from_issuer_public_key(ca_cert.public_key())
+    return x509.AuthorityKeyIdentifier.from_issuer_public_key(ca_cert.public_key())  # type: ignore[arg-type]
 
 
 def server_san() -> x509.SubjectAlternativeName:

tools/synchro.py

@@ -25,7 +25,7 @@
 from os import listdir
 from pathlib import Path
 
-from unasync import Rule, unasync_files  # type: ignore[import-not-found]
+from unasync import Rule, unasync_files  # type: ignore
 
 replacements = {
     "AsyncCollection": "Collection",