fix(ci): replace fake haskell-actions/setup SHA pin (#84)

## Summary

The pin `haskell-actions/setup@dd344bc1cec854a9b55c2b857c28b688010e4fce`
at `.github/workflows/e2e.yml:39` is fabricated. `gh api
repos/haskell-actions/setup/commits/dd344bc... → 422 "No commit found
for SHA"`.

The e2e job would have failed at action resolution on next run.

Replaced with verified v2.11.0 pin
`cd0d9bdd65b20557f41bea4dbe43d0b5fbbfe553`.

## Provenance

- Propagated from `rsr-template-repo`'s `e2e.yml` template (commented
stub uncommented when concretising here)
- Template fixed upstream: hyperpolymath/rsr-template-repo#81 (merged)
- Discovered while wiring CI for snifs: hyperpolymath/snifs#30
- Companion to: `panll#61`, `odds-and-sods-package-manager#39`,
`proven#93` (merged), `proven-servers#19`, and a throttled sweep of 16
commented-stub repos

## Test plan

- [ ] setup line uses `cd0d9bd...` (v2.11.0)
- [ ] `gh api
repos/haskell-actions/setup/commits/cd0d9bdd65b20557f41bea4dbe43d0b5fbbfe553`
returns 200
- [ ] The e2e job resolves its Haskell setup step instead of 422'ing

Author: hyperpolymath

.github/workflows/e2e.yml

@@ -36,7 +36,7 @@ jobs:
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4
 
       - name: Install Haskell (GHCup)
-        uses: haskell-actions/setup@dd344bc1cec854a9b55c2b857c28b688010e4fce  # v2
+        uses: haskell-actions/setup@cd0d9bdd65b20557f41bea4dbe43d0b5fbbfe553  # v2.11.0
         with:
           ghc-version: '9.6'
           cabal-version: '3.10'