test: improve CORS wildcard handling and testing

[appleboy]

• Add two new test functions in cors_test.go for parsing wildcard rules: one without wildcards and one with invalid wildcards
• Ensure no wildcard rules are returned when AllowWildcard is set to false
• Verify that parsing invalid wildcard rules triggers a panic

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.11%. Comparing base (fcbd06f) to head (37af0f5).

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #144 +/- ## ========================================== + Coverage 94.22% 95.11% +0.88% ========================================== Files 3 3 Lines 225 225 ========================================== + Hits 212 214 +2 + Misses 12 11 -1 + Partials 1 0 -1 ``` | [Flag](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | Coverage Δ | | |---|---|---| | [go-](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | `95.11% <ø> (+0.88%)` | :arrow_up: | | [go-1.18](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | `95.11% <ø> (+0.88%)` | :arrow_up: | | [go-1.19](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | `95.11% <ø> (+0.88%)` | :arrow_up: | | [go-1.20](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | `95.11% <ø> (+0.88%)` | :arrow_up: | | [go-1.21](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | `95.11% <ø> (+0.88%)` | :arrow_up: | | [go-1.22](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | `95.11% <ø> (+0.88%)` | :arrow_up: | | [macos-latest](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | `95.11% <ø> (+0.88%)` | :arrow_up: | | [ubuntu-latest](https://app.codecov.io/gh/gin-contrib/cors/pull/144/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib) | `95.11% <ø> (+0.88%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=gin-contrib#carryforward-flags-in-the-pull-request-comment) to find out more.

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