test_in_tail: relax too-tight timeouts in file-appended-after-start tests

[Watson1978]

Which issue(s) this PR fixes:
Fixes #

What this PR does / why we need it:

test_emit_with_read_lines_limit[flat 1] fails intermittently on CI (Ruby 3.4, windows-11-arm) with:

3) Failure: test_emit_with_read_lines_limit[flat 1](TailInputTest::singleline)
C:/a/fluentd/fluentd/test/plugin/test_in_tail.rb:509:in 'TailInputTest::TEST_VGFpbElucHV0VGVzdDo6c2luZ2xlbGluZQ#test_emit_with_read_lines_limit'
     506:       end
     507: 
     508:       events = d.events
  => 509:       assert_equal(true, events.length > 0)
     510:       assert_equal({"message" => msg}, events[0][2])
     511:       assert_equal({"message" => msg}, events[1][2])
     512:       assert num_events <= d.emit_count
<true> expected but was
<false>

diff:
? tru e
? fals 
? ??? 
Error: <true> expected but was
<false>.

https://github.com/fluent/fluentd/actions/runs/29549033055/job/87787458652#step:6:5460

i.e. no event was emitted within the 2s timeout.

These tests create/append the target file after d.run starts, so the new content is only picked up by the periodic refresh_watchers timer.
The first emit is therefore structurally pinned to ~1s regardless of machine speed, and timeout: 2 leaves only ~1s of margin.

A timeout threshold sweep (30 runs each) shows both macOS and Windows 11 ARM share the ~1s floor (0.8s always fails), but Windows has large jitter around it (13/30 fail at timeout 1.0s vs 0/30 on macOS). On the slower, more-contended windows-11-arm CI runner that jitter occasionally exceeds the 2s timeout, causing the flake.

expect_emits: returns as soon as the expected emits arrive (~1s), so raising the timeout does not slow the passing case; a real "no emit" regression is still caught, just after 10s instead of 2s.

Relax the timeouts of the three in_tail tests that share this "file activity after run starts + short timeout" shape:

• test_emit_with_read_lines_limit: 2 -> 10
• test_always_read_from_head_on_detecting_a_new_file: 3 -> 10
• test_watch_wildcard_path_without_watch_timer: 1 -> 10 (Linux-only, but had the tightest timeout)

Docs Changes:
N/A

Release Note:
N/A