GNOME comes with libsecret. You can use libsecret to store your git credentials:
sudo apt install libsecret-1-0 libsecret-1-dev libglib2.0-dev
sudo make --directory=/usr/share/doc/git/contrib/credential/libsecret
git config --global credential.helper /usr/share/doc/git/contrib/credential/libsecret/git-credential-libsecret