Add unix shebang for executables generated by analysis tests

See bazelbuild#18940 for more details. I've also wanted to update the tests, but it seems that this code doesn't have any test coverage (or I couldn't find it). To be fair, it is probably simple enough to not need it.

Closes bazelbuild#19780.

PiperOrigin-RevId: 572627238
Change-Id: I3685e782833712199a2696ac67477b9f2bb2f7ae

src/main/java/com/google/devtools/build/lib/analysis/test/AnalysisTestActionBuilder.java

@@ -47,6 +47,8 @@ public static void writeAnalysisTestAction(
     StringBuilder sb = new StringBuilder();
     if (ruleContext.isExecutedOnWindows()) {
       sb.append("@echo off\n");
+    } else {
+      sb.append("#!/bin/sh\n");
     }
     for (String line : Splitter.on("\n").split(escapedMessage)) {
       sb.append("echo ").append(line).append("\n");