[naga] Rename abstract-types snapshots abstract-types-const.

This prepares for introducing a similar test for global variables.

naga/tests/snapshots.rs

@@ -791,7 +791,7 @@ fn convert_wgsl() {
             Targets::SPIRV | Targets::GLSL | Targets::HLSL | Targets::WGSL,
         ),
         (
-            "abstract-types",
+            "abstract-types-const",
             Targets::SPIRV | Targets::METAL | Targets::GLSL | Targets::WGSL,
         ),
     ];