[BUG](api): fix grammar errors in validation error messages in types.py

## Problem
Several validation error messages in `chromadb/api/types.py` contain grammar errors:

1. **Line 1238:** `"an list"` → `"a list"` (in `validate_where` `$in/$nin` error)
2. **Line 1356:** `"a int"` → `"an int"` (in `validate_n_results` error)
3. **Line 1269:** `"those type"` → `"those types"` (in `validate_where` operand error)

## Affected Files
- `chromadb/api/types.py` — error message strings only, no logic changes

## Proposed Fix
Fix the three grammar errors in the error message strings.

Open chromadb/api/types.py and inspect the validation messages in validate_where and validate_n_results around lines 1238, 1269, and 1356. Correct the three grammatical errors without changing validation logic. Done means all three messages use the requested wording and the relevant validation behavior remains unchanged.

Written by the indexing model from the issue text.