fix: raise FileNotFoundError for missing TLS material (fixes #7564)

When a TLS certificate or key file is not found, the code currently
raises a generic OSError. This changes it to raise FileNotFoundError
with the proper errno (ENOENT) and filename attribute, which is more
specific and allows callers to catch this specific case.

FileNotFoundError is a subclass of OSError, so this is backward
compatible with existing code that catches OSError.

Author: Muhamed Fazal PS

src/requests/adapters.py

@@ -8,6 +8,7 @@
 
 from __future__ import annotations
 
+import errno
 import os.path
 import socket  # noqa: F401
 import typing
@@ -353,13 +354,17 @@ def cert_verify(
                 conn.cert_file = cert
                 conn.key_file = None
             if conn.cert_file and not os.path.exists(conn.cert_file):
-                raise OSError(
+                raise FileNotFoundError(
+                    os.strerror(errno.ENOENT),
                     f"Could not find the TLS certificate file, "
-                    f"invalid path: {conn.cert_file}"
+                    f"invalid path: {conn.cert_file}",
+                    conn.cert_file,
                 )
             if conn.key_file and not os.path.exists(conn.key_file):
-                raise OSError(
-                    f"Could not find the TLS key file, invalid path: {conn.key_file}"
+                raise FileNotFoundError(
+                    os.strerror(errno.ENOENT),
+                    f"Could not find the TLS key file, invalid path: {conn.key_file}",
+                    conn.key_file,
                 )
 
     def build_response(self, req: PreparedRequest, resp: Any) -> Response: