[FW][FIX] autocomplete: fix pivot group autocomplete

[fw-bot]

The computation to autocomplete pivot group values was only supporting string-like group values. If a user were to write some random input, like a number, the code would crash.

Task: 3976271

Description:

description of this task, what is implemented and why it is implemented that way.

Task: : TASK_ID

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_t("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

Forward-Port-Of: #4419

[robodoo]

[fw-bot]

@rrahir @pro-odoo this PR targets master and is the last of the forward-port chain.

To merge the full chain, use

@robodoo r+

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port

[pro-odoo]

robodoo r+