Sometimes, we have to access git repositories over SSL and the server only provides a self-signed certificate 🙈. Although there are ways to increase the trust level for the self-signed certificate (https://confluence.atlassian.com/fishkb/unable-to-clone-git-repository-due-to-self-signed-certificate-376838977.html, https://confluence.atlassian.com/bitbucketserverkb/resolving-ssl-self-signed-certificate-errors-806029899.html), my recommendation is to just ignore SSL verification alltogether.
Prepend GIT_SSL_NO_VERIFY=true before every git command run to skip SSL verification. This is particularly useful if you haven't checked out the repository yet.
Run git config http.sslVerify false to disable SSL verification if you're working with a checked out repository already.