The TestFileListing test in tplcontext_test has one test that verifies
if directory traversal is not happening. The context root is set to
'/tmp' and then it tries to open '../../../../../etc', which gets
normalized to '/tmp/etc'.
The test then expects an error to be returned, assuming that '/tmp/etc'
does not exist on the system. When it does exist, it results in a test
failure:
```
--- FAIL: TestFileListing (0.00s)
tplcontext_test.go:422: Test 4: Expected error but had none
FAIL
FAIL
github.com/caddyserver/caddy/v2/modules/caddyhttp/templates 0.042s
```
Instead of using '/tmp' as root, use a dedicated directory created with
`os.MkdirTemp()` instead. That way, we know that the directory is empty.
44e5e9e43f