fix(schematics): use a POSIX path for the Cloud Run main.js entry (#3274)

Running ng deploy from Windows with the Cloud Run SSR option wrote the
generated run/package.json entry paths with backslashes, which the
Linux-based Cloud Run runtime cannot resolve. The manifest path is now
built with forward slashes explicitly, since the target runtime is
Linux regardless of the deploying machine.

Fixes #3098

Co-authored-by: Armando Navarro <adnavarro@google.com>
(cherry picked from commit 73acea7)

Author: fr-esco

src/schematics/deploy/actions.ts

@@ -419,7 +419,8 @@ export const deployToCloudRun = async (
   fsHost.copySync(staticOut, newStaticOut);
   fsHost.copySync(serverOut, newServerOut);
 
-  const packageJson = getPackageJson(context, workspaceRoot, options, join(serverBuildOptions.outputPath, 'main.js'));
+  // Target runtime is Linux based.
+  const packageJson = getPackageJson(context, workspaceRoot, options, [serverBuildOptions.outputPath, 'main.js'].join('/'));
   const nodeVersion = packageJson.engines.node;
 
   if (!satisfies(process.versions.node, nodeVersion.toString())) {