Missing backport for generate_preset_pass_manager docs

[arnaucasau]

This PR fixes the docs for the generate_preset_pass_manager method. The main branch was changed to say Preset pass managers instead of A preset pass manager, so I'm bringing this change to stable/1.1.

This will need backport to stable/0.46 as well.

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[ElePT]

LGTM. It's not the easiest to keep track of all the backports.

[arnaucasau]

@Mergifyio backport stable/0.46

[mergify]

backport stable/0.46

❌ Command disallowed due to command restrictions in the Mergify configuration.

• sender-permission>=write

[arnaucasau]

Thanks for the review @ElePT! Could you trigger the Mergify for stable/0.46, please? I don't have enough permissions it seems 😓

[Eric-Arellano]

@mergify backport stable/0.46

[mergify]

backport stable/0.46

✅ Backports have been created

• #12638 Missing backport for generate_preset_pass_manager docs (backport #12636) has been created for branch stable/0.46