Fix errors finding Rust toolchain (#3802)

* switch to dtolnay/toolchain
* Add .dockerignore to avoid copying target/ into images
* update corrosion

.github/workflows/checks.yml

@@ -15,25 +15,25 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Cache cargo registry
-        uses: actions/cache@v4
-        with:
-          path: ~/.cargo/registry
-          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
-
-      - name: Cache cargo build
-        uses: actions/cache@v4
-        with:
-          path: target
-          key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
-
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
+        id: toolchain
         with:
           # If this version is old enough to cause errors, or older than the
           # TaskChampion MSRV, bump it to the MSRV of the currently-required
           # TaskChampion package; if necessary, bump that version as well.
           toolchain: "1.81.0" # MSRV
-          override: true
+
+      - name: Cache cargo registry
+        uses: actions/cache@v4
+        with:
+          path: ~/.cargo/registry
+          key: ${{ runner.os }}-cargo-registry-${{ steps.toolchain.outputs.cachekey }}-${{ hashFiles('**/Cargo.lock') }}
+
+      - name: Cache cargo build
+        uses: actions/cache@v4
+        with:
+          path: target
+          key: ${{ runner.os }}-cargo-build-target-${{ steps.toolchain.outputs.cachekey }}-${{ hashFiles('**/Cargo.lock') }}
 
       - uses: actions-rs/cargo@v1.0.3
         with:
@@ -53,12 +53,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
+        id: toolchain
         with:
-          profile: minimal
-          components: rustfmt
-          toolchain: stable
-          override: true
+          toolchain: "stable"
+          components: "rustfmt"
 
       - uses: actions-rs/cargo@v1.0.3
         with:
@@ -71,12 +70,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: actions-rs/toolchain@v1
+      - uses: dtolnay/rust-toolchain@master
+        id: toolchain
         with:
-          profile: minimal
-          components: rustfmt
-          toolchain: stable
-          override: true
+          toolchain: "stable"
+          components: "rustfmt"
 
       - name: "Check metadata"
         run: ".github/workflows/metadata-check.sh"