remove cache from GHA

It used to cache xargo, but Miri doesn't install xargo any more

Author: RalfJung

.github/workflows/ci.yml

@@ -15,13 +15,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/cache@v3
-        with:
-          path: |
-            ~/.cargo/bin/
-            ~/.cargo/.crates.toml
-            ~/.cargo/.crates2.json
-          key: ${{ runner.os }}-cargo-bin
       - name: Setup environment
         run: bash ./ci-setup.sh
       - name: Test
@@ -31,16 +24,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/cache@v3
-        with:
-          path: |
-            ~/.cargo/bin/
-            ~/.cargo/.crates.toml
-            ~/.cargo/.crates2.json
-          # FIXME: this does not work as intended!
-          # GHA caches are write-once, so if xargo updates we will keep having
-          # old xargo in our cache.
-          key: ${{ runner.os }}-cargo-bin
       - name: Setup environment
         run: bash ./ci-setup.sh
       - name: Test
@@ -50,16 +33,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/cache@v3
-        with:
-          path: |
-            ~/.cargo/bin/
-            ~/.cargo/.crates.toml
-            ~/.cargo/.crates2.json
-          # FIXME: this does not work as intended!
-          # GHA caches are write-once, so if xargo updates we will keep having
-          # old xargo in our cache.
-          key: ${{ runner.os }}-cargo-bin
       - name: Setup environment
         run: bash ./ci-setup.sh
       - name: Test
@@ -69,13 +42,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/cache@v3
-        with:
-          path: |
-            ~/.cargo/bin/
-            ~/.cargo/.crates.toml
-            ~/.cargo/.crates2.json
-          key: ${{ runner.os }}-cargo-bin
       - name: Setup environment
         run: bash ./ci-setup.sh
       - name: Test