Fix invalid links in blockchain roadmap (#6246)

Fixed broken links for "Visit the following relevant roadmaps". Backend redirected to javascript and Rust redirected to python.

src/data/roadmaps/blockchain/blockchain.json

@@ -5463,7 +5463,7 @@
       "selected": false,
       "data": {
         "label": "Rust",
-        "href": "https://roadmap.sh/python",
+        "href": "https://roadmap.sh/rust",
         "color": "#FFFFFf",
         "backgroundColor": "#4136D4",
         "style": {
@@ -5498,7 +5498,7 @@
       "selected": false,
       "data": {
         "label": "Backend",
-        "href": "https://roadmap.sh/javascript",
+        "href": "https://roadmap.sh/backend",
         "color": "#FFFFFf",
         "backgroundColor": "#4136D4",
         "style": {