infra: absolute `EXAMPLE_DIR` path in core unit tests (#16325)

If you invoked testing from places besides `core/`, this `EXAMPLE_DIR`
path won't work. This PR makes`EXAMPLE_DIR` robust against invocation
location

libs/core/tests/unit_tests/prompts/test_loading.py

@@ -10,7 +10,7 @@ from langchain_core.prompts.few_shot import FewShotPromptTemplate
 from langchain_core.prompts.loading import load_prompt
 from langchain_core.prompts.prompt import PromptTemplate
 
-EXAMPLE_DIR = Path("tests/unit_tests/examples").absolute()
+EXAMPLE_DIR = (Path(__file__).parent.parent / "examples").absolute()
 
 
 @contextmanager