templates: Using the variable on range scope `testCase` in function literal (scopelint)

```
templates/templates_test.go:74:29: Using the variable on range scope `testCase` in function literal (scopelint)
			assert.Check(t, is.Equal(testCase.expected, b.String()))
			                         ^
```

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

templates/templates_test.go

@@ -65,6 +65,8 @@ func TestParseTruncateFunction(t *testing.T) {
 	}
 
 	for _, testCase := range testCases {
+		testCase := testCase
+
 		tm, err := Parse(testCase.template)
 		assert.NilError(t, err)