brokers: Bump Go toolchain version to 1.24.12

[adombeck]

govulncheck reports the following vulnerabilities in go1.24.11

Vulnerability #1: GO-2026-4341
    Memory exhaustion in query parameter parsing in net/url
  More info: https://pkg.go.dev/vuln/GO-2026-4341
  Standard library
    Found in: net/[email protected]
    Fixed in: net/[email protected]
    Example traces found:
Error:       #1: internal/broker/broker.go:482:51: broker.Broker.generateUILayout calls oauth2.Config.DeviceAuth, which eventually calls url.ParseQuery
Error:       #2: internal/providers/msentraid/msmock_test.go:175:18: msentraid_test.mockMSServer.handleAuthorizeRequest calls url.URL.Query

Vulnerability #2: GO-2026-4340
    Handshake messages may be processed at the incorrect encryption level in
    crypto/tls
  More info: https://pkg.go.dev/vuln/GO-2026-4340
  Standard library
    Found in: crypto/[email protected]
    Fixed in: crypto/[email protected]
    Example traces found:
Error:       #1: internal/testutils/provider.go:104:14: testutils.StartMockProviderServer calls httptest.Server.Start, which eventually calls tls.Conn.HandshakeContext
Error:       #2: cmd/authd-oidc/daemon/daemon_test.go:211:18: daemon_test.TestAppCanSigHupWithoutExecute calls io.Copy, which eventually calls tls.Conn.Read
Error:       #3: cmd/authd-oidc/daemon/daemon_test.go:399:14: daemon_test.TestMain calls fmt.Fprintf, which calls tls.Conn.Write
Error:       #4: internal/broker/broker.go:482:51: broker.Broker.generateUILayout calls oauth2.Config.DeviceAuth, which eventually calls tls.Dialer.DialContext

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.57%. Comparing base (43be129) to head (e2a6329).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1233      +/-   ##
==========================================
- Coverage   87.61%   80.57%   -7.04%     
==========================================
  Files          91       20      -71     
  Lines        6231      978    -5253     
  Branches      111        0     -111     
==========================================
- Hits         5459      788    -4671     
+ Misses        716      190     -526     
+ Partials       56        0      -56     

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