Correctly handle EOF after unmatched backtick (#1187)

pkl-cli/src/test/kotlin/org/pkl/cli/repl/ReplMessagesTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -64,4 +64,11 @@ class ReplMessagesTest {
       startIndex = examples.indexOf("```", endIndex + 3)
     }
   }
+
+  @Test
+  fun `handle single backtick`() {
+    val responses = server.handleRequest(ReplRequest.Eval("1", "`", true, true))
+    assertThat(responses.size).isEqualTo(1)
+    assertThat(responses).hasOnlyElementsOfType(ReplResponse.EvalError::class.java)
+  }
 }