Fix let do/end block definitions with keyword overlap

Example:

```
let(:todo) do # "do" keyword overlap
  {
    'todo' => 'end' # "end" keyword overlap
  }
end
```

lib/solargraph/rspec/spec_walker/fake_let_method.rb

@@ -5,16 +5,17 @@ module Rspec
     class SpecWalker
       class FakeLetMethod
         MATCH_BODY = Regexp.union(
-          /do(.*)end/m,
+          /.* do(.*)end/m,
           /{(.*)}/m
         )
 
         # @param block_ast [RubyVM::AbstractSyntaxTree::Node]
-        # @return [RubyVM::AbstractSyntaxTree::Node]
+        # @return [RubyVM::AbstractSyntaxTree::Node, nil]
         def self.transform_block(block_ast, code, method_name = nil)
           method_name ||= NodeTypes.let_method_name(block_ast)
           block_body = block_ast.children[1]
-          matches = code.lines[block_body.first_lineno - 1..block_body.last_lineno - 1].join.match(MATCH_BODY)
+          let_definition_code = code.lines[block_body.first_lineno - 1..block_body.last_lineno - 1].join
+          matches = let_definition_code.match(MATCH_BODY)
           method_body = (matches[1] || matches[2]).strip
 
           ast = RubyVM::AbstractSyntaxTree.parse <<~RUBY

spec/solargraph/rspec/convention_spec.rb

@@ -95,6 +95,42 @@
     expect(completion_at(filename, [22, 8])).to include('nested_something')
   end
 
+  it 'generates let methods with do/end block' do
+    load_string filename, <<~RUBY
+      RSpec.describe SomeNamespace::Transaction, type: :model do
+        let(:something) do
+          "something"
+        end
+
+        let!(:other_thing) do
+          2
+        end
+
+        let(:todo) do # "do" keyword overlap
+          {
+            'todo' => 'end' # "end" keyword overlap
+          }
+        end
+      end
+    RUBY
+
+    assert_public_instance_method_inferred_type(
+      api_map,
+      'RSpec::ExampleGroups::TestSomeNamespaceTransaction#something',
+      'String'
+    )
+    assert_public_instance_method_inferred_type(
+      api_map,
+      'RSpec::ExampleGroups::TestSomeNamespaceTransaction#other_thing',
+      'Integer'
+    )
+    assert_public_instance_method_inferred_type(
+      api_map,
+      'RSpec::ExampleGroups::TestSomeNamespaceTransaction#todo',
+      'Hash'
+    )
+  end
+
   it 'generates implicit subject method' do
     load_string filename, <<~RUBY
       RSpec.describe SomeNamespace::Transaction, type: :model do