ci: explicitly cache .rustup

Addresses issue reported in:

- jdx/mise-action#215
- jdx/mise-action#184

Author: auxesis

.github/workflows/test-eql.yml

@@ -48,6 +48,15 @@ jobs:
           cache: true # [default: true] cache mise using GitHub's cache
           cache_key_prefix: "mise-v3"
 
+      - name: Cache Rust directories
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.rustup
+          key: rust-cache-${{ runner.os }}-${{ hashFiles('mise.toml') }}
+          restore-keys: |
+            rust-cache-${{ runner.os }}-
+
       - name: Setup database (Postgres ${{ matrix.postgres-version }})
         run: |
           mise run postgres:up postgres-${POSTGRES_VERSION} --extra-args "--detach --wait"