[HttpKernel] Replace sha1 with sha256 in recently added tests

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | -
| License       | MIT

Tests were introduced in #10896 and are broken starting with 2.4, since the hashing algorithm has changed (introduced in #8609).