Fix code scanning alert no. 1: Use of insecure SSL/TLS version (#25)

Fixes
[https://github.com/andreasgriffin/bitcoin-safe/security/code-scanning/1](https://github.com/andreasgriffin/bitcoin-safe/security/code-scanning/1)

To fix the problem, we need to ensure that the SSL context explicitly
disallows insecure TLS versions and only allows TLS 1.2 or higher. This
can be done by setting the `minimum_version` attribute of the SSL
context to `ssl.TLSVersion.TLSv1_2`.

The best way to fix the problem without changing existing functionality
is to modify the SSL context creation in the
`get_electrum_server_version` function. Specifically, we will set the
`minimum_version` attribute of the context to `ssl.TLSVersion.TLSv1_2`
right after creating the context with `ssl.create_default_context()`.


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bitcoin_safe/gui/qt/network_settings/main.py

@@ -93,6 +93,7 @@ def get_electrum_server_version(host: str, port: int, use_ssl: bool = True, time
             ssock: Optional[socket.socket] = None
             if use_ssl:
                 context = ssl.create_default_context()
+                context.minimum_version = ssl.TLSVersion.TLSv1_2
                 ssock = context.wrap_socket(sock, server_hostname=host)
             else:
                 ssock = sock