Update and pin GitHub actions (#211)

Using `pinact run --update`

<https://github.com/suzuki-shunsuke/pinact>

Also: dependabot will continue functioning as usual, and it also knows
how to update the version comments.

.github/workflows/rust-tests.yml

@@ -39,21 +39,21 @@ jobs:
           --health-retries 5
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
 
       - name: Cache cargo registry
-        uses: actions/cache@v5
+        uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
         with:
           path: ~/.cargo/registry
           key: ${{ runner.os }}-${{ matrix.rust }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
 
       - name: Cache cargo build
-        uses: actions/cache@v5
+        uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # v5.0.5
         with:
           path: target
           key: ${{ runner.os }}-${{ matrix.rust }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
 
-      - uses: actions-rs/toolchain@v1
+      - uses: actions-rs/toolchain@b2417cde72dcf67f306c0ae8e0828a81bf0b189f # v1.0.6
         with:
           toolchain: "${{ matrix.rust }}"
           override: true