ci: use the container-structure-test image instead of a pinned download

The pinned release URL returned 404. test/run.sh already falls back to the
official tool image when the binary is absent, so CI and local runs now take
the same path.

Also pin *.txt to LF and make the required-features lookup tolerate CRLF, so
the feature gate works on a Windows checkout too.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Agent-Id: agent-7034f75b-1ddc-4aa1-a4ea-3a54b340e8d9

.github/workflows/test.yml

@@ -39,12 +39,8 @@ jobs:
       - name: Build test image
         run: docker build -t restic-backup-docker:test .
 
-      - name: Install container-structure-test
-        run: |
-          curl -fsSL -o /usr/local/bin/container-structure-test \
-            https://storage.googleapis.com/container-structure-test/v1.19.3/container-structure-test-linux-amd64
-          chmod +x /usr/local/bin/container-structure-test
-
+      # container-structure-test is not installed: test/run.sh falls back to
+      # the official tool image, which keeps CI and local runs identical.
       - name: Run test suites
         run: bash test/run.sh --no-build