The integer primary key is not included in the information_schema.tidb_index_usage

[YangKeao]

I recorded the index usage of clustered primary keys and integer primary keys in #55602, but when the primary key is an integer, it'll not show in the Index list of TableInfo, so it doesn't appear in the information_schema.tidb_index_usage table 🤦 .

My fault. The previous PR doesn't have any E2E test.

[YangKeao]

I'll cherry-pick the fix to release-8.5, as this function doesn't work without this fix.

[YangKeao]

Here is a simple reproduce:

CREATE TABLE t (pk INT PRIMARY KEY);

SELECT * FROM information_schema.tidb_index_usage WHERE table_schema = 'test';

The primary key is not included in it.