impr(ci): use hetzner buckets for cache (#11364)

## Problem
Occasionally getting data from GH cache could be slow, with less than
10MB/s and taking 5+ minutes to download cache:
```
Received 20971520 of 2987085791 (0.7%), 9.9 MBs/sec
Received 50331648 of 2987085791 (1.7%), 15.9 MBs/sec
...
Received 1065353216 of 2987085791 (35.7%), 4.8 MBs/sec
Received 1065353216 of 2987085791 (35.7%), 4.7 MBs/sec
...
```

https://github.com/neondatabase/neon/actions/runs/13956437454/job/39068664599#step:7:17

Resulting in getting cache even longer that build time.

## Summary of changes
Switch to the caches, that are closer to the runners, and they provided
stable throughput about 70-80MB/s

.github/workflows/_check-codestyle-python.yml

@@ -37,8 +37,14 @@ jobs:
 
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
 
-      - uses: actions/cache@d4323d4df104b026a6aa633fdb11d772146be0bf # v4.2.2
+      - name: Cache poetry deps
+        uses: tespkg/actions-cache@b7bf5fcc2f98a52ac6080eb0fd282c2f752074b1  # v1.8.0
         with:
+          endpoint: ${{ vars.HETZNER_CACHE_REGION }}.${{ vars.HETZNER_CACHE_ENDPOINT }}
+          bucket: ${{ vars.HETZNER_CACHE_BUCKET }}
+          accessKey: ${{ secrets.HETZNER_CACHE_ACCESS_KEY }}
+          secretKey: ${{ secrets.HETZNER_CACHE_SECRET_KEY }}
+          use-fallback: false
           path: ~/.cache/pypoetry/virtualenvs
           key: v2-${{ runner.os }}-${{ runner.arch }}-python-deps-bookworm-${{ hashFiles('poetry.lock') }}