build.yml: Fix 'Print failure info' to not error

Print Failure Info is for printing differences detected by 'Test all'.  When some other step fails, then "*.exp" doesn't match any files at all, and _this_ step fails too.

Following https://stackoverflow.com/questions/4839214/does-ash-have-an-equivalent-to-bashs-nullglob-option detect when "*.exp" doesn't match anything and avoid an error.

This is hard to test, so testing performed: Looked at 7 lines of shell script and was unable to see any problems.

This is an alternative to #4334, which would remove the step entirely. It is undesirable to do that, as we wouldn't be able to see the information about the failures that occurred anymore.

Author: jepler

.github/workflows/build.yml

@@ -81,7 +81,9 @@ jobs:
       working-directory: tests
     - name: Print failure info
       run: |
-        for exp in *.exp;
+        set -- ./*.exp
+        [ -e "$1" ] || shift
+        for exp;
         do testbase=$(basename $exp .exp);
         echo -e "\nFAILURE $testbase";
         diff -u $testbase.exp $testbase.out;