switch from Jest to Vitest

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

__tests__/.setup/list-itg-tests.mjs

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+/**
+ * Copyright 2026 actions-toolkit authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import fs from 'node:fs';
+import path from 'node:path';
+
+const testsRoot = path.resolve('__tests__');
+const results = [];
+
+const walk = dir => {
+  for (const entry of fs.readdirSync(dir, {withFileTypes: true})) {
+    const fullPath = path.join(dir, entry.name);
+    if (entry.isDirectory()) {
+      walk(fullPath);
+      continue;
+    }
+    if (entry.isFile() && entry.name.endsWith('.test.itg.ts')) {
+      results.push(fullPath.replaceAll(path.sep, '/'));
+    }
+  }
+};
+
+walk(testsRoot);
+results.sort((a, b) => a.localeCompare(b));
+process.stdout.write(`${results.join('\n')}\n`);

__tests__/.setup/setup.itg.ts

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+/**
+ * Copyright 2026 actions-toolkit authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {vi} from 'vitest';
+
+vi.mock('@actions/github');

__tests__/.setup/setup.unit.ts

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+/**
+ * Copyright 2026 actions-toolkit authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import {vi} from 'vitest';
+
+const envTmpDir = process.env.DOCKER_ACTIONS_TOOLKIT_TMPDIR;
+const tmpDir = envTmpDir || fs.mkdtempSync(path.join(os.tmpdir(), 'docker-actions-toolkit-'));
+
+vi.mock('@actions/github');
+
+process.env = Object.assign({}, process.env, {
+  DOCKER_ACTIONS_TOOLKIT_TMPDIR: tmpDir,
+  TEMP: tmpDir,
+  GITHUB_REPOSITORY: 'docker/actions-toolkit',
+  GITHUB_RUN_ATTEMPT: '2',
+  GITHUB_RUN_ID: '2188748038',
+  GITHUB_RUN_NUMBER: '15',
+  RUNNER_TEMP: path.join(tmpDir, 'runner-temp'),
+  RUNNER_TOOL_CACHE: path.join(tmpDir, 'runner-tool-cache')
+});