Upgrade tree-sitter-php to v0.21.1 (#6902)

This PR upgrades `tree-sitter-php` to v0.21.1.

Here is the diff between our current version and this version:
d43130fd15...29a49d3a53

The primary impetus for this change is to get this change that adds the
`license` field to the `Cargo.toml`:
https://github.com/tree-sitter/tree-sitter-php/pull/193

This will silence the warning that is shown when running
`script/generate-licenses`.

Release Notes:

- Upgraded `tree-sitter-php` to v0.21.1.

crates/semantic_index/src/semantic_index_tests.rs

@@ -1546,7 +1546,7 @@ fn php_lang() -> Arc<Language> {
                 collapsed_placeholder: "/* ... */".into(),
                 ..Default::default()
             },
-            Some(tree_sitter_php::language()),
+            Some(tree_sitter_php::language_php()),
         )
         .with_embedding_query(
             r#"