tests(run): add spec tests for non-executable entrypoints (#34779)

Adds characterization spec tests for two `deno run` error paths where
the command-line entrypoint can't be executed as an ES module. The
existing run specs cover missing modules and import-*statement*
resolution, but not these entrypoint cases.

New spec dir `tests/specs/run/entrypoint_errors`:

| entrypoint | error |
| --- | --- |
| a directory | `ERR_UNSUPPORTED_DIR_IMPORT` (no index resolution for
file: ESM entrypoints, even when the dir contains a module) |
| a `.json` file | rejected — JSON needs an explicit `with { type:
"json" }` attribute, which a bare entrypoint can't supply |

Each asserts exit code 1 and the error output (the directory path is
wildcarded). Test-only change; no runtime behavior is affected.

Author: crowlbot

tests/specs/run/entrypoint_errors/__test__.jsonc

@@ -0,0 +1,14 @@
+{
+  "tests": {
+    "directory_entrypoint": {
+      "args": "run subdir",
+      "output": "error: [ERR_UNSUPPORTED_DIR_IMPORT] Directory import 'file://[WILDCARD]/subdir' is not supported resolving ES modules\n",
+      "exitCode": 1
+    },
+    "json_entrypoint": {
+      "args": "run data.json",
+      "output": "error: Attempted to load JSON module without specifying \"type\": \"json\" attribute in the import statement.\n",
+      "exitCode": 1
+    }
+  }
+}

tests/specs/run/entrypoint_errors/data.json

@@ -0,0 +1 @@
+{ "name": "x" }

tests/specs/run/entrypoint_errors/subdir/mod.ts

@@ -0,0 +1 @@
+console.log("hi");