Added H2 title for list reports in 'All reports' page

[lucascumsille]

Fixes: https://github.com/mysociety/societyworks/issues/4239

This is a title we have added to improve accessibility and avoid the jumping from h1 straight to h3

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.66%. Comparing base (ce80472) to head (e4dfe85).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5052 +/- ## ======================================= Coverage 82.65% 82.66% ======================================= Files 396 396 Lines 30828 30828 Branches 4890 4890 ======================================= + Hits 25482 25483 +1 + Misses 3900 3899 -1 Partials 1446 1446 ```

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