git ephemeral directories sometimes not being cleaned up

Hi,

As explained to me by William:

| ephemeral-* directories are a hardlink farm used for MP diffs. They're meant to be deleted within a few seconds.

Unfortunately, it seems like they're not always being cleaned up:

| ubuntu@juju-86e177-prod-turku-6:/media/turku_storage_2-turku_storage/07b54da4-eeb0-41ed-8ce8-5e5dca2e3759/git.snapshots/latest$ ls ephemeral* -lad | tail -n 20
| drwxr-xr-x 6 1002 1002 4096 Oct 29 2018 ephemeral-fec30772479d4004bb1e8284f474b5d8
| drwxr-xr-x 6 1002 1002 4096 Sep 18 2020 ephemeral-fec31f23cdda4c1baaa5b6e010441dc1
| drwxr-xr-x 6 1002 1002 4096 Jun 28 2021 ephemeral-fec4c1a887fc44a6badcfa748504951b
| drwxr-xr-x 6 1002 1002 4096 Apr 21 2021 ephemeral-fec9a0eed32541898e6f82b70827f884
| drwxr-xr-x 6 1002 1002 4096 Jul 28 2021 ephemeral-fedffec6e2934b0a8089e4c3452f1c69
| drwxr-xr-x 6 1002 1002 4096 Sep 19 2020 ephemeral-fee759ef9d0f40ddb9bf11ef6485bf69
| drwxr-xr-x 6 1002 1002 4096 Jun 16 2021 ephemeral-fef8cdce0d37479c818b8d19b481dd42
| drwxr-xr-x 6 1002 1002 4096 Aug 11 2020 ephemeral-fef99ecdd1a647d09d94844f0d4559fd
| drwxr-xr-x 6 1002 1002 4096 Dec 21 2017 ephemeral-ff15c18b298f4d0d8cb7c8f1e7924146
| drwxr-xr-x 6 1002 1002 4096 Nov 14 2019 ephemeral-ff41765d0c2f40f3ac69c086cd662dea
| drwxr-xr-x 6 1002 1002 4096 Apr 30 2021 ephemeral-ff5ecfa3aca147f190738a1b0a0a7e2f
| drwxr-xr-x 6 1002 1002 4096 Feb 14 2019 ephemeral-ff714a2196be4b4c8428cdb20197cbf9
| drwxr-xr-x 6 1002 1002 4096 Oct 5 2020 ephemeral-ff816125a1404fce9179d9845241085c
| drwxr-xr-x 6 1002 1002 4096 Jul 18 2016 ephemeral-ff99955e5ff3494fb6eb2911d4dea5d3
| drwxr-xr-x 6 1002 1002 4096 Aug 3 2019 ephemeral-ffb0a860c42541f9ab8628d13fdcf929
| drwxr-xr-x 6 1002 1002 4096 Apr 21 2021 ephemeral-ffb9563632fe4cb4b2dba8677fd24466
| drwxr-xr-x 6 1002 1002 4096 Apr 30 2021 ephemeral-ffba2c44b881411d90c401c7831b31e6
| drwxr-xr-x 6 1002 1002 4096 Sep 18 2020 ephemeral-ffc579b2475f4415b052ae9c7917e6ba
| drwxr-xr-x 6 1002 1002 4096 Jun 28 2021 ephemeral-ffc6972576334386a9dc3cd40d76e056
| drwxr-xr-x 6 1002 1002 4096 Jul 5 2019 ephemeral-fff920d784e24cff9e0a44cc559d08d4

| ubuntu@juju-86e177-prod-turku-6:/media/turku_storage_2-turku_storage/07b54da4-eeb0-41ed-8ce8-5e5dca2e3759/git.snapshots/latest$ ls ephemeral* -lad | wc -l
| 3705