Resolve issue where standalone return statemente incorrectly expected an expression

Author: ahoppen

Sources/SwiftParser/Statements.swift

@@ -865,7 +865,7 @@ extension Parser {
     let expr: RawExprSyntax?
     if
       !self.at(any: [
-        RawTokenKind.rightBrace, .semicolon, .eof,
+        .rightBrace, .caseKeyword, .semicolon, .eof,
         .poundIfKeyword, .poundErrorKeyword, .poundWarningKeyword,
         .poundEndifKeyword, .poundElseKeyword, .poundElseifKeyword
       ])

Tests/SwiftParserTest/Statements.swift

@@ -251,7 +251,7 @@ final class StatementTests: XCTestCase {
       ]
     )
   }
-  
+
   func testIfHasSymbol() {
     AssertParse(
       """