Expect indented case block instead of match stmt (#11033)

## Summary

This PR adds a new `Clause::Case` and uses it to parse the body of a
`case` block. Earlier, it was using `Match` which would give an
incorrect error message like:

```
  |
1 | match subject:
2 |     case 1:
3 |     case 2: ...
  |     ^^^^ Syntax Error: Expected an indented block after `match` statement
  |
```

## Test Plan

Add test case and update the snapshot.

crates/ruff_python_parser/resources/inline/err/case_expect_indented_block.py

@@ -0,0 +1,3 @@
+match subject:
+    case 1:
+    case 2: ...