chore: keep the line endings LF

Everything but dependencies.json is stored with LF, which nothing said, so
a CRLF file could get in unnoticed (it did, for two files, in a round trip
that shows as a rewrite of every line of both).

* .gitattributes: normalize every text file to LF in the repository and
  check it out with LF, whatever core.autocrlf is (the Windows runner
  defaults it to true)
* rustfmt.toml: newline_style = "Unix", so cargo fmt --check fails on
  a Rust file with CRLF
* CI: fail when a file is stored with CRLF
* dependencies.json: the one file that was stored with CRLF

.github/workflows/windows.yaml

@@ -54,6 +54,10 @@ jobs:
           cache-on-failure: "true"
           cache-all-crates: "true"
           key: ${{ matrix.platform.target }}
+      - name: Check that no file is stored with CRLF
+        run: |
+          $crlf = git ls-files --eol | Select-String -Pattern '^i/crlf'
+          if ($crlf) { $crlf; exit 1 }
       - run: cargo +nightly fmt --check
       - run: cargo clippy
       - run: cargo test