Submodules, by definition, always refer to a specific SHA1 in a subproject. That SHA1 is not expressed in the .gitmodules file, but instead is expressed as a record in a tree object that contains a submodule. The way you install this in git is cd in the submodule, checking the SHA1 you want, then cd goes back to the parent repo and commits your change, which will appear just like the changed file.
So, in your case, what you can do is
cd vendor/plugins/ssl_requirement git checkout bc96ad96407a72a60e0542cf3b0cecc6ff9e278e cd .. git add ssl_requirement
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