fix: Remove use of boolean value for metrics properties (#29315)

## **Description**

Remove use of boolean value for metrics property.

## **Related issues**

Fixes: MetaMask/MetaMask-planning#3811

## **Manual testing steps**
NA

## **Screenshots/Recordings**
NA

## **Pre-merge author checklist**

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- [X] I've completed the PR template to the best of my ability
- [X] I’ve included tests if applicable
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- [X] I’ve applied the right labels on the PR (see [labeling
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Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

ui/pages/confirmations/hooks/useTrackERC20WithoutDecimalInformation.ts

@@ -39,7 +39,7 @@ const useTrackERC20WithoutDecimalInformation = (
           event: MetaMetricsEventName.SimulationIncompleteAssetDisplayed,
           category: MetaMetricsEventCategory.Confirmations,
           properties: {
-            token_decimals_available: false,
+            token_decimals_available: 'not_available',
             asset_address: tokenAddress,
             asset_type: TokenStandard.ERC20,
             chain_id: chainId,