[llvm] [lit] Fix to make "RUN: env PATH=..." work as intended (PR #165308)

[Björn Pettersson via llvm-commits]

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@@ -1,7 +1,7 @@
 ## Tests env command for setting the PATH variable.
 
 # The test is using /bin/sh. Limit to system known to have /bin/sh.
-# REQUIRED: system-linux
+# REQUIRES: system-linux
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bjope wrote:

Is perhaps `REQUIRES: shell` more appropriate?

https://github.com/llvm/llvm-project/pull/165308