Fix session state

Session state must be set only once:

```py
if "is_shared" not in st.session_state:
st.session_state["is_shared"] = False
```

otherwise the `st.session_state["is_shared"] = False` is run on each page reload. This is how streamlit works (each time to interact with the UI, the all page is rerun). I tested it locally and it should work now :)

app.py

@@ -68,7 +68,9 @@ model_info = "N/A"
 ### Conversion factors
 kg_per_mile = 0.348
 embodied_conversion_factor = 0.0289
-st.session_state["is_shared"] = False
+
+if "is_shared" not in st.session_state:
+    st.session_state["is_shared"] = False
 
 electricity = pd.read_csv(electricity_url)
 servers = pd.read_csv(server_url)
@@ -190,7 +192,7 @@ div.stButton > button:first-child {
 
 buttoncol1, buttoncol2, buttoncol3 = st.columns(3)
 with buttoncol2:
-    if st.session_state["is_shared"] == False:
+    if not st.session_state["is_shared"]:
         submitted = st.button(label="Share my CO2 data!", on_click = lambda *args: write_to_csv(hardware, gpu_tdp, num_gpus, training_time, provider, carbon_intensity, dynamic_emissions, experimentation_time, experimental_emissions, pue, pue_emissions, embodied_type, embodied_emissions, model_info))
     else:
         st.info('Thank you! Your data has been shared in https://huggingface.co/datasets/sasha/co2_submissions.')