Core: fix Anthropic json issue in streaming (#16670)

**Description:** fix ChatAnthropic json issue in streaming 
**Issue:** https://github.com/langchain-ai/langchain/issues/16423
**Dependencies:** n/a

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

libs/core/langchain_core/output_parsers/json.py

@@ -138,7 +138,7 @@ def parse_json_markdown(
         The parsed JSON object as a Python dictionary.
     """
     # Try to find JSON string within triple backticks
-    match = re.search(r"```(json)?(.*)```", json_string, re.DOTALL)
+    match = re.search(r"```(json)?(.*)(```)?", json_string, re.DOTALL)
 
     # If no match found, assume the entire string is a JSON string
     if match is None:

libs/core/tests/unit_tests/output_parsers/test_json.py

@@ -137,6 +137,43 @@ TEXT_BEFORE_AND_AFTER = """Action: Testing
 ```
 This should do the trick"""
 
+WITHOUT_END_BRACKET = """Here is a response formatted as schema:
+
+```json
+{
+  "foo": "bar"
+  
+
+"""
+
+WITH_END_BRACKET = """Here is a response formatted as schema:
+
+```json
+{
+  "foo": "bar"
+}
+  
+"""
+
+WITH_END_TICK = """Here is a response formatted as schema:
+
+```json
+{
+  "foo": "bar"
+}
+``` 
+"""
+
+WITH_END_TEXT = """Here is a response formatted as schema:
+
+```
+{
+  "foo": "bar"
+
+``` 
+This should do the trick 
+"""
+
 TEST_CASES = [
     GOOD_JSON,
     JSON_WITH_NEW_LINES,
@@ -148,6 +185,10 @@ TEST_CASES = [
     TEXT_BEFORE,
     TEXT_AFTER,
     TEXT_BEFORE_AND_AFTER,
+    WITHOUT_END_BRACKET,
+    WITH_END_BRACKET,
+    WITH_END_TICK,
+    WITH_END_TEXT,
 ]