docs: fix trim for rust,ignore blocks

[Jefffrey]

Which issue does this PR close?

Issue was raised as comment: #17913 (comment)

Rationale for this change

On current website can see:

• https://datafusion.apache.org/library-user-guide/upgrading.html#projectionexpr-changed-from-type-alias-to-struct

Source document:

datafusion/docs/source/library-user-guide/upgrading.md

Lines 204 to 218 in 408e1e4

	**Before:**
	```rust,ignore
	pub type ProjectionExpr = (Arc<dyn PhysicalExpr>, String);
	```
	**After:**
	```rust,ignore
	#[derive(Debug, Clone)]
	pub struct ProjectionExpr {
	pub expr: Arc<dyn PhysicalExpr>,
	pub alias: String,
	}
	```

-https://datafusion.apache.org/library-user-guide/extending-operators.html#optimizing-logical-plan

Source document:

datafusion/docs/source/library-user-guide/extending-operators.md

Lines 32 to 57 in 408e1e4

	```rust,ignore
	fn rewrite(
	&self,
	plan: LogicalPlan,
	_config: &dyn OptimizerConfig,
	) -> Result<Transformed<LogicalPlan>> {
	// Attempts to rewrite a logical plan to a uwheel-based plan that either provides
	// plan-time aggregates or skips execution based on min/max pruning.
	if let Some(rewritten) = self.try_rewrite(&plan) {
	Ok(Transformed::yes(rewritten))
	} else {
	Ok(Transformed::no(plan))
	}
	}
	```
	```rust,ignore
	// Converts a uwheel aggregate result to a TableScan with a MemTable as source
	fn agg_to_table_scan(result: f64, schema: SchemaRef) -> Result<LogicalPlan> {
	let data = Float64Array::from(vec![result]);
	let record_batch = RecordBatch::try_new(schema.clone(), vec![Arc::new(data)])?;
	let df_schema = Arc::new(DFSchema::try_from(schema.clone())?);
	let mem_table = MemTable::try_new(schema, vec![vec![record_batch]])?;
	mem_table_as_table_scan(mem_table, df_schema)
	}
	```

,ignore should also be trimmed out.

What changes are included in this PR?

Fix regex used in trimming rust blocks to account for optional ignore.

Are these changes tested?

Tested locally:

Existing blocks (with only rust and not rust,ignore) unaffected, e.g. in catalogs page:

Are there any user-facing changes?

No, doc changes.

[Weijun-H]

👍