Merge pull request #14940 from NixOS/backport-14778-to-2.30-maintenance

[Backport 2.30-maintenance] test: add shebangs to shell.nix test scripts

tests/functional/shell.nix

@@ -96,14 +96,16 @@ let
 
     foo = runCommand "foo" { } ''
       mkdir -p $out/bin
-      echo 'echo ${fooContents}' > $out/bin/foo
+      echo '#!${shell}' > $out/bin/foo
+      echo 'echo ${fooContents}' >> $out/bin/foo
       chmod a+rx $out/bin/foo
       ln -s ${shell} $out/bin/bash
     '';
 
     bar = runCommand "bar" { } ''
       mkdir -p $out/bin
-      echo 'echo bar' > $out/bin/bar
+      echo '#!${shell}' > $out/bin/bar
+      echo 'echo bar' >> $out/bin/bar
       chmod a+rx $out/bin/bar
     '';
 
@@ -116,7 +118,8 @@ let
     # ruby "interpreter" that outputs "$@"
     ruby = runCommand "ruby" { } ''
       mkdir -p $out/bin
-      echo 'printf %s "$*"' > $out/bin/ruby
+      echo '#!${shell}' > $out/bin/ruby
+      echo 'printf %s "$*"' >> $out/bin/ruby
       chmod a+rx $out/bin/ruby
     '';