refactor: enable cargo's sparse protocol in ci

for now until rust 1.70.0

https://blog.rust-lang.org/2023/03/09/Rust-1.68.0.html#cargos-sparse-protocol

.cirrus.yml

@@ -9,6 +9,8 @@ task:
   only_if: $CIRRUS_TAG == ''
   env:
     RUSTFLAGS: -Dwarnings
+    # Cargo's sparse protocol from 1.68.0 onwards
+    CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
   matrix:
     - name: freebsd-amd64-test
       env:
@@ -41,6 +43,8 @@ task:
   only_if: $CIRRUS_TAG != ''
   env:
     RUSTFLAGS: -Dwarnings
+    # Cargo's sparse protocol from 1.68.0 onwards
+    CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
     GITHUB_TOKEN: ENCRYPTED[d1766ef328d83729917d2ffb875d64c35d1c0177edf8f32e66ec464daf5c1b7b145d65fc6c044a73fffe2235d3b38349]
   matrix:
     - name: freebsd-amd64-release

.github/workflows/devel.yml

@@ -14,6 +14,8 @@ jobs:
     name: test
     runs-on: ${{ matrix.os }}
     env:
+      # Cargo's sparse protocol from 1.68.0 onwards
+      CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
       CARGO_BIN: cargo
       # When CARGO_BIN is set to CROSS, this is set to `--target matrix.target`
       TARGET_FLAGS: ""
@@ -148,11 +150,17 @@ jobs:
         echo "SKIP_TESTS=yes" >> $GITHUB_ENV
 
     - name: Run tests
+      shell: bash
       if: env.SKIP_TESTS == ''
-      run: ${{ env.CARGO_BIN }} test --verbose ${{ env.TARGET_FLAGS }}
+      run: |
+        if [[ "${{ matrix.build }}" == "pinned" ]]; then unset CARGO_REGISTRIES_CRATES_IO_PROTOCOL; fi
+        ${{ env.CARGO_BIN }} test --verbose ${{ env.TARGET_FLAGS }}
 
     - name: Run build
-      run: ${{ env.CARGO_BIN }} build --verbose ${{ env.TARGET_FLAGS }}
+      shell: bash
+      run: |
+        if [[ "${{ matrix.build }}" == "pinned" ]]; then unset CARGO_REGISTRIES_CRATES_IO_PROTOCOL; fi
+        ${{ env.CARGO_BIN }} build --verbose ${{ env.TARGET_FLAGS }}
 
   checks:
     name: checks

.github/workflows/release.yml

@@ -37,6 +37,8 @@ jobs:
     needs: ['create-release']
     runs-on: ${{ matrix.os }}
     env:
+      # Cargo's sparse protocol from 1.68.0 onwards
+      CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
       # For some builds, we use cross to test on 32-bit and big-endian
       # systems.
       CARGO_BIN: cargo