ci: Fix invalid syntax in missing ops workflow (#109)

Looks like this job has been failing since the last time I changed it
-.-

I ways trying to pas an `env` var into the `secrets` of the workflow
call,
which caused a syntax error.

https://github.com/CQCL/tket-json-rs/actions/runs/12348388888

.github/workflows/missing-ops.yml

@@ -45,16 +45,18 @@ jobs:
         run: |
           set +e
           uv run -- cargo test --test integration -- --ignored missing_optypes --nocapture --test-threads=1 > missing_optypes.txt
+          cat missing_optypes.txt
+          echo
           if [ $? -eq 0 ]; then
             echo "The test passed."
             echo "fail=false" >> $GITHUB_OUTPUT
           else
             echo "The test failed with error code $?."
-            echo
-            cat missing_optypes.txt
             echo "fail=true" >> $GITHUB_OUTPUT
           fi
-          echo "diagnostic=$(cat missing_optypes.txt)" >> $GITHUB_OUTPUT
+          echo "diagnostic<<EOF" >> $GITHUB_OUTPUT
+          cat missing_optypes.txt >> $GITHUB_OUTPUT
+          echo "EOF" >> $GITHUB_OUTPUT
 
   create-issue:
     uses: CQCL/hugrverse-actions/.github/workflows/create-issue.yml@main
@@ -66,12 +68,11 @@ jobs:
             ⚠️ `tket-json-rs` is missing OpType definitions.
 
             ```
-            $DIAGNOSTIC
+            ${{ needs.missing-optypes.outputs.diagnostic }}
             ```
 
             See [https://github.com/CQCL/tket-json-rs/actions/runs/${{ github.run_id }}](the failing check) for more info.
         unique-label: "missing-ops"
         other-labels: "bug"
     secrets:
         GITHUB_PAT: ${{ secrets.HUGRBOT_PAT }}
-        DIAGNOSTIC: ${{ needs.missing-optypes.outputs.diagnostic }}