Gracefully handle entrypoint permission errors (#15026)
Gracefully handle entrypoint permission errors
`uv run --with` could fail with a "permission denied" error when it
tried to copy an entrypoint with restrictive permissions.
For instance:
```sh
$ stat -c '%A' /usr/bin/groupmems
-rwxr-s---
$ uv python find
/usr/bin/python
$ uv run --with dummy_test
error: failed to open file `/usr/bin/groupmems`: Permission denied (os error 13)
```
The entrypoint copying logic now catches these permission errors and
skips the file, making `uv` more resilient on systems with binaries that
have restrictive permissions.
