Add JetBrains fallback tests and tighten URL assertions

Agent-Logs-Url: https://github.com/AKB0700/setup-java/sessions/b5ff7a8f-7d53-4825-9148-a3d7b9163aac

Co-authored-by: AKB0700 <157992575+AKB0700@users.noreply.github.com>

__tests__/distributors/jetbrains-installer.test.ts

@@ -54,6 +54,61 @@ describe('getAvailableVersions', () => {
       os.platform() === 'win32' ? manifestData.length : manifestData.length + 2;
     expect(availableVersions.length).toBe(length);
   }, 10_000);
+
+  it('uses _nomod package URL when base package is unavailable', async () => {
+    spyHttpClient.mockReturnValueOnce({
+      statusCode: 200,
+      headers: {},
+      result: [{tag_name: 'jbr-release-21.0.3b465.3', prerelease: true}] as any
+    });
+    spyHttpClient.mockReturnValueOnce({
+      statusCode: 200,
+      headers: {},
+      result: []
+    });
+    jest
+      .spyOn(HttpClient.prototype, 'head')
+      .mockResolvedValueOnce({message: {statusCode: 404}} as any)
+      .mockResolvedValueOnce({message: {statusCode: 200}} as any);
+
+    const distribution = new JetBrainsDistribution({
+      version: '21-ea',
+      architecture: 'x64',
+      packageType: 'jdk',
+      checkLatest: false
+    });
+    const availableVersions = await distribution['getAvailableVersions']();
+
+    expect(availableVersions).toHaveLength(1);
+    expect(availableVersions[0].url).toContain('_nomod-21.0.3-linux-x64-b465.3');
+  });
+
+  it('filters out versions when both package URLs are unavailable', async () => {
+    spyHttpClient.mockReturnValueOnce({
+      statusCode: 200,
+      headers: {},
+      result: [{tag_name: 'jbr-release-21.0.3b465.3', prerelease: true}] as any
+    });
+    spyHttpClient.mockReturnValueOnce({
+      statusCode: 200,
+      headers: {},
+      result: []
+    });
+    jest
+      .spyOn(HttpClient.prototype, 'head')
+      .mockResolvedValueOnce({message: {statusCode: 404}} as any)
+      .mockResolvedValueOnce({message: {statusCode: 404}} as any);
+
+    const distribution = new JetBrainsDistribution({
+      version: '21-ea',
+      architecture: 'x64',
+      packageType: 'jdk',
+      checkLatest: false
+    });
+    const availableVersions = await distribution['getAvailableVersions']();
+
+    expect(availableVersions).toHaveLength(0);
+  });
 });
 
 describe('findPackageForDownload', () => {
@@ -89,7 +144,7 @@ describe('findPackageForDownload', () => {
       const resolvedVersion =
         await distribution['findPackageForDownload'](input);
       expect(resolvedVersion.url).toMatch(
-        /^https:\/\/cache-redirector\.jetbrains\.com\/intellij-jbr\//
+        /^https:\/\/cache-redirector\.jetbrains\.com\/intellij-jbr\/.+-b\d+(\.\d+)?\.tar\.gz$/
       );
     }
   );