ci: Don't print output twice in ci-util

Use `tee` rather than printing to both stdout and stderr.

library/compiler-builtins/.github/workflows/main.yaml

@@ -34,7 +34,7 @@ jobs:
       - name: Fetch pull request ref
         run: git fetch origin "$GITHUB_REF:$GITHUB_REF"
         if: github.event_name == 'pull_request'
-      - run: python3 ci/ci-util.py generate-matrix >> "$GITHUB_OUTPUT"
+      - run: set -e; python3 ci/ci-util.py generate-matrix | tee "$GITHUB_OUTPUT"
         id: script
 
   test:

library/compiler-builtins/ci/ci-util.py

@@ -282,8 +282,6 @@ class Context:
         may_skip = str(self.may_skip_libm_ci()).lower()
         print(f"extensive_matrix={ext_matrix}")
         print(f"may_skip_libm_ci={may_skip}")
-        eprint(f"extensive_matrix={ext_matrix}")
-        eprint(f"may_skip_libm_ci={may_skip}")
         eprint(f"total extensive tests: {total_to_test}")
 
         if error_on_many_tests and total_to_test > PrCfg.MANY_EXTENSIVE_THRESHOLD: