`cabal exec` does not accept relative or absolute paths

**To Reproduce**
```
$ echo "echo foo" > foo.sh
$ chmod +x foo.sh
$ ./foo.sh
foo
```

```
$ cabal exec ./foo.sh
Error: [Cabal-6666]
The program './foo.sh' is required but it could not be found.
```

```
$ cabal --version
cabal-install version 3.11.0.0
compiled using version 3.11.0.0 of the Cabal library
```

Start by reproducing the issue with the provided foo.sh commands and the reported Cabal version, then trace the cabal exec entry point and its handling of the program path. Done means cabal exec accepts both ./foo.sh and an absolute path and runs the script successfully.

Written by the indexing model from the issue text.