Backport(v1.19): test: fix unused ports outside the OS dynamic port range (#5451)

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Which issue(s) this PR fixes:
Backport #5451
Fixes #

What this PR does / why we need it:
On Windows, Hyper-V/WinNAT/HNS take their reservations from the dynamic port range, which is 49152-65535 as observed on GitHub Actions runners, and a reservation can appear between the check and the actual bind.

When searching for unused ports, this PR will avoid this range to prevent following error.

3) Error: test: send_with_time_as_integer(ForwardOutputTest): Errno::EACCES: Permission denied - bind(2) for 127.0.0.1:58707
C:/hostedtoolcache/windows/Ruby/4.0.5/arm64/lib/ruby/4.0.0/socket.rb:183:in 'Socket#bind'
C:/hostedtoolcache/windows/Ruby/4.0.5/arm64/lib/ruby/4.0.0/socket.rb:183:in 'Addrinfo#bind'
C:/a/fluentd/fluentd/lib/fluent/plugin_helper/server.rb:402:in 'Fluent::PluginHelper::Server#server_create_udp_socket'
C:/a/fluentd/fluentd/lib/fluent/plugin_helper/server.rb:178:in 'Fluent::PluginHelper::Server#server_create'
C:/a/fluentd/fluentd/lib/fluent/plugin/in_forward.rb:192:in 'Fluent::Plugin::ForwardInput#start'
C:/a/fluentd/fluentd/lib/fluent/test/driver/base.rb:120:in 'Fluent::Test::Driver::Base#instance_start'
C:/a/fluentd/fluentd/lib/fluent/test/driver/base.rb:78:in 'Fluent::Test::Driver::Base#run'
C:/a/fluentd/fluentd/lib/fluent/test/driver/base_owner.rb:130:in 'Fluent::Test::Driver::BaseOwner#run'
C:/a/fluentd/fluentd/test/plugin/test_out_forward.rb:516:in 'block (2 levels) in <class:ForwardOutputTest>'
C:/hostedtoolcache/windows/Ruby/4.0.5/arm64/lib/ruby/gems/4.0.0/gems/test-unit-rr-1.0.5/lib/test/unit/rr.rb:98:in 'Test::Unit::RR::Adapter#assert_rr'
C:/a/fluentd/fluentd/test/plugin/test_out_forward.rb:515:in 'block in <class:ForwardOutputTest>'

https://github.com/fluent/fluentd/actions/runs/29884012909/job/88810722450#step:6:5337

Related to #5434

Docs Changes:
N/A

Release Note:
N/A