Auto merge of #12020 - crepererum:fix/shebang, r=aneeshusa

Add shebang to Linux runservo.sh

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Shebang is missing and therefore `./runservo.sh` does not work under some environments.

I've chosen to use `/usr/bin/env sh` instead of `/bin/sh` or `/usr/bin/sh` to auto-select the right `sh` executable depending on the environment.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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- [X] These changes do not require tests because it does not affect servo itself but rather the resulting package under some environments.

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python/servo/package_commands.py

@@ -177,7 +177,7 @@ class PackageCommands(CommandBase):
                           path.join('./build/' + browserhtml_path.split('/')[-1], 'out', 'index.html')]
 
             runservo = os.open(dir_to_package + '/runservo.sh', os.O_WRONLY | os.O_CREAT, int("0755", 8))
-            os.write(runservo, "./servo " + ' '.join(servo_args))
+            os.write(runservo, "#!/usr/bin/env sh\n./servo " + ' '.join(servo_args))
             os.close(runservo)
             print("Creating tarball")
             tar_path = '/'.join(dir_to_package.split('/')[:-1]) + '/'