Prevent some warnings when building the documentation.
Prevent some warnings when building the documentation.

Indeed, we used to get three warnings that read `Duplicate explicit target name: "here"`.
```
cellml/libcellml,nickerso/libcellml,cellml/libcellml,hsorby/libcellml,hsorby/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,cellml/libcellml,nickerso/libcellml,hsorby/libcellml,nickerso/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml