Renovate: Pin the SnakeYaml dependency

Stick to version 1.31, which is the latest version that does not limit
the file size to 3 MiB, also see the discussion at [1].

[1]: oss-review-toolkit/ort#5818

Signed-off-by: Sebastian Schuberth <[email protected]>

Author: sschuberth

renovate.json

@@ -6,7 +6,8 @@
   "packageRules": [
     {
       "matchPackageNames": [
-        "org.jetbrains.kotlin.jvm"
+        "org.jetbrains.kotlin.jvm",
+        "org.yaml:snakeyaml"
       ],
       "rangeStrategy": "pin"
     }