Fix binary file matching in test_wasm_opt (#8440)

```py
binary = '.wasm' in t
```
can incorrectly also match when the directory name contains it, like,
`~/binaryen.wasm_split/...`.

Author: aheejin

scripts/test/wasm_opt.py

@@ -50,7 +50,7 @@ def test_wasm_opt():
         if ('translate-to-fuzz' in t or 'dwarf' in t) and \
            shared.skip_if_on_windows('fuzz translation tests'):
             continue
-        binary = '.wasm' in t
+        binary = t.endswith('.wasm')
         base = os.path.basename(t).replace('.wast', '').replace('.wasm', '')
         passname = base
         passes_file = os.path.join(shared.get_test_dir('passes'), passname + '.passes')