test(slider): add slider related tests

[PBK-B]

🤔 这个 PR 的性质是？

• 日常 bug 修复
• 新特性提交
• 文档改进
• 演示代码改进
• 组件样式/交互改进
• CI/CD 改进
• 重构
• 代码风格优化
• 测试用例
• 分支合并
• 其他

🔗 相关 Issue

#1280

💡 需求背景和解决方案

• test(slider): add slider tests
• fix(slider): 修复点击 marks 触发 cannot read properties of null 异常（在测试中发现的）

📝 更新日志

• 本条 PR 不需要纳入 Changelog

☑️ 请求合并前的自查清单

⚠️ 请自检并全部勾选全部选项。⚠️

• 文档已补充或无须补充
• 代码演示已提供或无须提供
• TypeScript 定义已补充或无须补充
• Changelog 已提供或无须提供

[github-actions]

[codecov-commenter]

Codecov Report

Merging #1297 (3b59d39) into develop (9fde83a) will increase coverage by 0.38%.
The diff coverage is 56.75%.

@@             Coverage Diff             @@
##           develop    #1297      +/-   ##
===========================================
+ Coverage    59.78%   60.16%   +0.38%     
===========================================
  Files         1017     1017              
  Lines        17806    17805       -1     
  Branches      4083     4083              
===========================================
+ Hits         10645    10713      +68     
+ Misses        7161     7092      -69     

Impacted Files	Coverage Δ
src/cascader/Cascader.tsx	57.89% <0.00%> (ø)
src/color-picker/ColorPicker.tsx	84.21% <ø> (ø)
src/date-picker/DateRangePicker.tsx	10.00% <0.00%> (ø)
src/date-picker/base/Header.tsx	43.83% <ø> (ø)
src/date-picker/panel/RangePanel.tsx	82.22% <ø> (-0.76%)	⬇️
src/form/_example/align.jsx	80.00% <0.00%> (ø)
src/form/_example/base.jsx	53.84% <ø> (ø)
src/form/_example/layout.jsx	80.00% <0.00%> (ø)
src/input-number/_example/center.jsx	44.44% <ø> (ø)
src/input-number/_example/large-number.jsx	100.00% <ø> (ø)
... and 39 more

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