[stable18] Increase from 100000 to 600000 iterations for hash_pbkdf2

[come-nc]

Backport of #39024

[come-nc]

/backport to stable17

[come-nc]

/backport to stable16

[backportbot-nextcloud]

The backport to stable16 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable16
git pull origin stable16

# Create the new backport branch
git checkout -b fix/foo-stable16

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable16

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport