add test reference for an error message

Signed-off-by: Aryan Gupta <garyan447@gmail.com>

Author: aryangupta701

tests/errors/test_optional.py

@@ -0,0 +1,2 @@
+def match(pat : str, string : str) -> Optional[list[str] | str]:
+    return None

tests/reference/asr-test_optional-97e5371.json

@@ -0,0 +1,13 @@
+{
+    "basename": "asr-test_optional-97e5371",
+    "cmd": "lpython --show-asr --no-color {infile} -o {outfile}",
+    "infile": "tests/errors/test_optional.py",
+    "infile_hash": "2532c73de47afb82c9d1d9fa335d3b274e7c79a14007353639958a45",
+    "outfile": null,
+    "outfile_hash": null,
+    "stdout": null,
+    "stdout_hash": null,
+    "stderr": "asr-test_optional-97e5371.stderr",
+    "stderr_hash": "b9cc75eb200847db5d4d39d9f511959ebf22faad68cf0096c7a2b68c",
+    "returncode": 2
+}

tests/reference/asr-test_optional-97e5371.stderr

@@ -0,0 +1,5 @@
+semantic error: The type 'Optional' is undeclared.
+ --> tests/errors/test_optional.py:1:39
+  |
+1 | def match(pat : str, string : str) -> Optional[list[str] | str]:
+  |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^ 

tests/tests.toml

@@ -1383,3 +1383,7 @@ run_with_dbg = true
 [[test]]
 filename = "runtime_errors/test_raise_01.py"
 run_with_dbg = true
+
+[[test]]
+filename = "errors/test_optional.py"
+asr = true