⚰️ Remove Python 3.8 from CI and remove Python 3.8 examples from source docs (#14559)

Co-authored-by: Yurii Motov <yurii.motov.monte@gmail.com>
Co-authored-by: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>

docs_src/debugging/tutorial001_py39.py

@@ -0,0 +1,15 @@
+import uvicorn
+from fastapi import FastAPI
+
+app = FastAPI()
+
+
+@app.get("/")
+def root():
+    a = "a"
+    b = "b" + a
+    return {"hello world": b}
+
+
+if __name__ == "__main__":
+    uvicorn.run(app, host="0.0.0.0", port=8000)