Update CI to Godot 3.5.1-stable

Author: Bromeon

.github/workflows/full-ci.yml

@@ -276,13 +276,13 @@ jobs:
         include:
           # Latest Godot with different Rust versions
           - rust: stable
-            godot: "3.5.1-rc1"
+            godot: "3.5.1-stable"
             postfix: ''
           - rust: nightly
-            godot: "3.5.1-rc1"
+            godot: "3.5.1-stable"
             postfix: ' (nightly)'
           - rust: '1.63'
-            godot: "3.5.1-rc1"
+            godot: "3.5.1-stable"
             postfix: ' (msrv 1.63)'
 
           # Test with oldest supported engine version

.github/workflows/minimal-ci.yml

@@ -12,7 +12,7 @@ env:
 
   # Local variables
   # Note: using variables is limited at the moment, see https://github.com/actions/runner/issues/480
-  GODOT_VER: "3.5.1-rc1"
+  GODOT_VER: "3.5.1-stable"
 
   # Don't use more features like "gdnative_bindings_generator/debug" to keep CI truly minimal
   GDRUST_FEATURES: "gdnative/async,gdnative/serde"