Keep project recoveries from 6.9 onwards separate

[jclarkeSTFC]

The format of the project recovery folder changed in 6.9, see #36859. This PR changes the project recovery folder so that pre-6.9 and 6.9-onwards backups are kept separate. This fixes a bug where if you tried to start 6.9 with a backup from 6.8, Workbench would not open.

Description of work

• Changed name of project recovery folder

To test:

• Follow all testing instructions in Change project recovery to save one recovery script rather than one for each workspace #36859
• Open 6.8 (or earlier), load at least one file (otherwise a backup won't be created), wait for a backup to be created.
• Deliberately crash 6.8 (Segfault algorithm)
• Open 6.9.
• Try the above but with the opposite version order.

Fixes #36900

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[thomashampson]

Something weird was happening when I tested this. I crashed 6.9 and 6.8, then recovered 6.9 successfully. But when I opened 6.8, it recovered the 6.9 workspaces from the ordered_recovery.py file, rather than looking in the workbench-recovery directory

[jclarkeSTFC]

Got a better fix in #36914