CI: fix remaining Flow error in spm-ios-e2e.js execFileSync env

execFileSync's `env` option is invariantly typed {[string]: string |
number | void}, so neither a plain process.env spread ({[string]: string
| void}) nor a string-only object satisfies it. Build the env object
into a correctly-typed indexer instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: chrfalch

scripts/e2e/spm-ios-e2e.js

@@ -109,36 +109,27 @@ function step(msg /*: string */) {
   console.log(`\n\x1b[35m==> ${msg}\x1b[0m`);
 }
 
-// process.env is typed to allow numbers, but execFileSync's `env` option wants
-// string values only — copy across just the string entries.
-function stringEnv() /*: {[string]: string} */ {
-  const out /*: {[string]: string} */ = {};
-  for (const key of Object.keys(process.env)) {
-    const value = process.env[key];
-    if (typeof value === 'string') {
-      out[key] = value;
-    }
-  }
-  return out;
-}
-
 function run(
   cmd /*: string */,
   args /*: Array<string> */,
   cwd /*: string */,
   env /*:: ?: {[string]: string} */,
 ) /*: void */ {
   console.log(`$ (cd ${cwd} && ${cmd} ${args.join(' ')})`);
-  // With no override, omit `env` so execFileSync inherits process.env as-is.
+  // execFileSync's `env` option is invariantly typed as
+  // {[string]: string | number | void}. process.env is {[string]: string | void}
+  // and our overrides are strings, so a plain spread's narrower type is rejected;
+  // build the object into a correctly-typed indexer instead.
+  const childEnv /*: {[string]: string | number | void} */ = {};
+  for (const key of Object.keys(process.env)) {
+    childEnv[key] = process.env[key];
+  }
   if (env != null) {
-    execFileSync(cmd, args, {
-      cwd,
-      stdio: 'inherit',
-      env: {...stringEnv(), ...env},
-    });
-  } else {
-    execFileSync(cmd, args, {cwd, stdio: 'inherit'});
+    for (const key of Object.keys(env)) {
+      childEnv[key] = env[key];
+    }
   }
+  execFileSync(cmd, args, {cwd, stdio: 'inherit', env: childEnv});
 }
 
 function resolveInRepoApp(app /*: 'rntester' | 'helloworld' */) /*: AppMeta */ {