fix: plugins cors allow_origins is "**" work does not meet expectations

[kys1230]

Description

Resolved an issue where the cross-origin plugin did not function correctly when the plugin configuration allow_origins = "**" and an exceptional request header Origin contained a comma (",").

Checklist

• [x] I have explained the need for this PR and the problem it solves
• [x] I have explained the changes or the new features added to this PR
• [ ] I have added tests corresponding to this change
• [ ] I have updated the documentation to reflect this change
• [ ] I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)