Git SSH Urls cannot select a branch

When using envbuilder with a git ssh url we cannot target a specific branch. Tracing this through it's because of the giturls library succeeds in parsing a transport/http regex and gleans the url fragment and this is mapped to a branch in coder. However for ssh no fragment is parsed in the scpProvider regex. Presumably it would be good to have a way similar to https to signal to coder a branch we want to check out. If this can't be done via the Git url then perhaps another env var / parameter needs to be available to achieve this

从 giturls 的解析路径开始，尤其是 scpProvider regex，并将其与 transport/http 的解析以及 coder 如何将 URL 片段映射到分支进行比较。确认 SSH URL 或其他参数如何表达所请求的分支，然后验证基于 SSH 的 envbuilder 构建会检出该分支。

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