Stabilize ruby:3.4/sinatra-1.4 matrix by hardening SSL connection spec isolation

[Copilot]

The matrix / test (ruby:3.4, sinatra-1.4) job was failing due to a cascade from verify_server_cert specs in connection_spec: an unexpected TLS transport error caused one example to fail while WebMock remained disabled, which then broke many unrelated specs.

• Root-cause containment in verify_server_cert specs

  • Wrapped WebMock.disable! sections with begin ... ensure ... end so WebMock is always re-enabled, even when the example raises.
  • Prevents global test state leakage and downstream false failures.

• Expectation scope tightened for verify_server_cert: false

  • Updated the negative logger assertion to target certificate-verification failures only (instead of broad SSL_connect matching), aligning the check with what the example intends to prove.

• Illustrative change

  WebMock.disable!
  begin
    subject.write('')
    subject.flush
  ensure
    WebMock.enable!
  end

[hegerchr]

LGTM