docs: release-1.5 backup-classes.md omits FoundationDB from the endpoint TLS-enabling sentence #3365

Context

Follow-up recommended in the review of cozystack/website#622 (cozystack/website#622 (review)).

Problem

On release-1.5, docs/operations/backup-classes.md (the endpoint knob row, line 138) says switching the endpoint to https:// enables TLS only in the MariaDB strategy:

endpoint | S3 endpoint baked into every default strategy CR + the Velero BSL. Switching to https:// silently enables TLS in the MariaDB strategy — ensure the CA bundle is reachable to the relevant operator/driver Pods before flipping it.

This omits FoundationDB. The FoundationDB strategy template derives urlParameters.secure_connection from the endpoint scheme identically on main and release-1.5, so flipping the scheme affects FDB backups the same way.

Both other copies of this doc already have it right:

• main's docs/operations/backup-classes.md says "MariaDB/FoundationDB strategies";
• the website's v1.5 page (from fix(backup): simplify UX with default backupclass and correct the admin override path (next + v1.5) website#622) says "MariaDB/FoundationDB strategies".

Only the release-1.5 in-repo copy is behind, so the two v1.5 copies will drift apart.

Fix

One-line change on release-1.5, docs/operations/backup-classes.md:138: "in the MariaDB strategy" → "in the MariaDB/FoundationDB strategies".