fix: prevent duplicate cross installation when cache restored

Issue: Cache restore-keys can restore from partial match (e.g., 'Linux-cross-')
but cache-hit is only 'true' for exact key matches. This caused the install
step to run even when cross binary was already cached, resulting in error:
'binary cross already exists in destination'

Fix: Add explicit check for cross binary existence before attempting install
Uses 'command -v cross' to detect if binary is available regardless of how
it was restored (exact cache hit or restore-keys match)

This ensures the install step only runs when cross is truly not available.

Author: tazarov

.github/actions/setup-cross-compilation/action.yml

@@ -27,8 +27,19 @@ runs:
         restore-keys: |
           ${{ runner.os }}-cross-
 
+    - name: Check if cross is already installed
+      id: check-cross
+      shell: bash
+      run: |
+        if command -v cross &> /dev/null; then
+          echo "installed=true" >> $GITHUB_OUTPUT
+          echo "cross is already installed: $(cross --version)"
+        else
+          echo "installed=false" >> $GITHUB_OUTPUT
+        fi
+
     - name: Install cross
-      if: steps.cache-cross.outputs.cache-hit != 'true'
+      if: steps.check-cross.outputs.installed != 'true'
       shell: bash
       run: |
         # Install cross from crates.io (stable release)