[cd] Bump CIRCT from firtool-1.75.0 to firtool-1.121.0

This is an automated commit generated by the `circt/update-circt` GitHub
Action.

Author: bar-tender

conda-reqs/circt.json

@@ -1,3 +1,3 @@
 {
-  "version": "firtool-1.75.0"
+  "version": "firtool-1.121.0"
 }