Rename expectation files to contain only one dot.
This is needed for the Cython tests as of Cython 3.
The following script was used in a clean repository
to rename the files:
```sh
ls | sed -E -n 's/(.*)\.(both|tag)?((\..*)?\.(c|cpp|pyx))/mv "\1.\2\3" "\1_\2\3"/p' | sh
```
