fix(ci): replace fake goto-bus-stop/setup-zig SHA pin (2 sites) (#93)

## Summary

The pin
`goto-bus-stop/setup-zig@7ab2955eb728f5440978d7b4f723a50dea1f3608` at
`.github/workflows/e2e.yml:46,157` is fabricated. `gh api
repos/goto-bus-stop/setup-zig/commits/7ab2955... → 422 "No commit found
for SHA"`.

The fake SHA's first 16 hex chars happen to collide with v2.2.0's real
SHA `7ab2955eb728f5440978d5824358023be3a2802d`, but the rest is
fabricated — making this an especially subtle failure to catch by eye.
Whoever introduced the pin likely mistyped or hallucinated the suffix.

Replaced with verified v2.2.1 pin
`abea47f85e598557f500fa1fd2ab7464fcb39406`.

## 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
- 2 of 3 fan-out PRs (alongside `odds-and-sods-package-manager#39` and
`proven-servers` incoming)

## Test plan

- [ ] Both setup-zig lines in diff use `abea47f85e...` (v2.2.1)
- [ ] `gh api
repos/goto-bus-stop/setup-zig/commits/abea47f85e598557f500fa1fd2ab7464fcb39406`
returns 200
- [ ] The e2e workflow's Zig setup step actually resolves instead of
422'ing on next run

Author: hyperpolymath

.github/workflows/e2e.yml

@@ -43,7 +43,7 @@ jobs:
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4
 
       - name: Install Zig
-        uses: goto-bus-stop/setup-zig@7ab2955eb728f5440978d7b4f723a50dea1f3608  # v2
+        uses: goto-bus-stop/setup-zig@abea47f85e598557f500fa1fd2ab7464fcb39406  # v2.2.1
         with:
           version: 0.15.0
 
@@ -154,7 +154,7 @@ jobs:
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4
 
       - name: Install Zig
-        uses: goto-bus-stop/setup-zig@7ab2955eb728f5440978d7b4f723a50dea1f3608  # v2
+        uses: goto-bus-stop/setup-zig@abea47f85e598557f500fa1fd2ab7464fcb39406  # v2.2.1
         with:
           version: 0.15.0