gatsby-remark-images : bug: uses filename as alt text when showCaptions is true

gatsby-remark-images : bug: uses filename as alt text when showCaptions is true: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). Description Since https://github.com/gatsbyjs/gatsby/pull/13489, when using showCaptions:true gatsby-remark-images inserts the file name, when…