[ci] switch to explicit hashes for taiki-e/install-action

The renovate/pin-dependencies task was failing on this.

.github/workflows/coverage.yml

@@ -25,9 +25,13 @@ jobs:
  - uses: Swatinem/rust-cache@23bce251a8cd2ffc3c1075eaa2367cf899916d84 # v2
 
  - name: Install latest nextest release
- uses: taiki-e/install-action@nextest
+ uses: taiki-e/install-action@a94d7ba8955e0861119ed8d3fddb8823ef7a97a8 # v2
+ with:
+ tool: nextest
  - name: Install cargo-llvm-cov
- uses: taiki-e/install-action@cargo-llvm-cov
+ uses: taiki-e/install-action@a94d7ba8955e0861119ed8d3fddb8823ef7a97a8 # v2
+ with:
+ tool: cargo-llvm-cov
 
  - name: Collect coverage data
  # Generate separate reports for nextest and doctests, and combine them.