fix: Avoid "Argument list too long" when setting results output (#79)

This PR updates the “Set results output” step so data from previous
steps is directly interpolated into the JS script, rather than passed
via environment variables. This prevents “Argument list too long” errors
(and resulting workflow failures).

Under the hood, `actions/github-script` was doing something like this:

```shell
FILINGS='/** A huge JSON blob **/' FIXINGS='/** A huge JSON blob **/' node tmp/script.js
```

Depending on the size of `FILINGS` and `FIXINGS`, this could exceed a
system’s `ARG_MAX` (https://www.in-ulm.de/~mascheck/various/argmax/ is a
good explainer).

After removing the environment variables, the argument list length is
much shorter, so the error is avoided.

Author: smockle

action.yml

@@ -109,8 +109,8 @@ runs:
       uses: actions/github-script@v8
       with:
         script: |
-          const filings = JSON.parse(process.env.FILINGS || '[]');
-          const fixings = JSON.parse(process.env.FIXINGS || '[]');
+          const filings = ${{ steps.file.outputs.filings || '""' }} || [];
+          const fixings = ${{ steps.fix.outputs.fixings || '""' }} || [];
           const fixingsByIssueUrl = fixings.reduce((acc, fixing) => {
             if (fixing.issue && fixing.issue.url) {
               acc[fixing.issue.url] = fixing;
@@ -125,9 +125,6 @@ runs:
           }
           core.setOutput('results', JSON.stringify(results));
           core.debug(`Results: ${JSON.stringify(results)}`);
-      env:
-        FILINGS: ${{ steps.file.outputs.filings }}
-        FIXINGS: ${{ steps.fix.outputs.fixings }}
     - name: Save cached results
       uses: ./../../_actions/github/accessibility-scanner/current/.github/actions/gh-cache/cache
       with: