lib: internal/errors should not be executable

PR-URL: #16369
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Timothy Gu <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Gibson Fahnestock <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Gireesh Punathil <[email protected]>