Docs: update build.tools versions

Follows #10217

Author: humitos

docs/user/config-file/v2.rst

@@ -348,6 +348,7 @@ Node.js version to use.
    - ``16``
    - ``18``
    - ``19``
+   - ``20``
 
 build.tools.rust
 ````````````````
@@ -359,6 +360,7 @@ Rust version to use.
    - ``1.55``
    - ``1.61``
    - ``1.64``
+   - ``1.70``
 
 build.tools.golang
 ``````````````````
@@ -370,6 +372,7 @@ Go version to use.
    - ``1.17``
    - ``1.18``
    - ``1.19``
+   - ``1.20``
 
 build.apt_packages
 ``````````````````

readthedocs/rtd_tests/fixtures/spec/v2/schema.json

@@ -187,19 +187,25 @@
                   "enum": [
                     "14",
                     "16",
-                    "18"
+                    "18",
+                    "19",
+                    "20"
                   ]
                 },
                 "rust": {
                   "enum": [
                     "1.55",
-                    "1.61"
+                    "1.61",
+                    "1.64",
+                    "1.70"
                   ]
                 },
                 "golang": {
                   "enum": [
                     "1.17",
-                    "1.18"
+                    "1.18",
+                    "1.19",
+                    "1.20"
                   ]
                 }
               },