Get --repo_env=NAME value from client environment (not server).

Fixes issue where server process would "cache" environment variables. Broken since 3ebf658 (v5).

Closes #24433.

PiperOrigin-RevId: 698847238
Change-Id: I51d4ec811ee9d78717ff816d9988b4ad0f533265

src/main/java/com/google/devtools/build/lib/runtime/CommandEnvironment.java

@@ -340,7 +340,7 @@ public void exit(AbruptExitException exception) {
       String name = entry.getKey();
       String value = entry.getValue();
       if (value == null) {
-        value = System.getenv(name);
+        value = clientEnv.get(name);
       }
       if (value != null) {
         repoEnv.put(name, value);