clippy: fix warnings introduced with Rust 1.78

[cakebaker]

This PR fixes the clippy warnings introduced with Rust 1.78. In two cases I used #[allow(clippy::assigning_clones)] because the suggested changes didn't work.

[cakebaker]

Changes since last push:

• fixed warning in df unit test

[sylvestre]

the suggested changes didn't work.

do you have details ?
it might interest @samueltardieu

[cakebaker]

Changes since last push:

• reversed change from previous push, used #[allow(assigning_clones)] instead

[samueltardieu]

Indeed, it looks like assigning_clones is a false positive here, as the entity is reassigned to the result of a computation on itself and is thus borrowed. I'll check that this has been properly registered as a bug on Clippy's side.

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/timeout/timeout is no longer failing!