ci: Actually enable incremental building (despite the default in rust-cache)

.github/workflows/test_rust.yml

@@ -78,6 +78,9 @@ jobs:
         # See: https://github.com/nextest-rs/nextest/issues/1172
         run: cargo nextest run --cargo-profile ci --workspace --locked --no-fail-fast --retries 2 -j 4 --features imgtests,lzma,jpegxr
         env:
+          # This is to counteract the disabling by rust-cache.
+          # See: https://github.com/Swatinem/rust-cache/issues/43
+          CARGO_INCREMENTAL: '1'
           # Supposedly makes "Updating crates.io index" faster on Windows.
           # See: https://github.com/rust-lang/cargo/issues/9167
           CARGO_NET_GIT_FETCH_WITH_CLI: 'true'

Cargo.toml

@@ -103,4 +103,5 @@ inherits = "release"
 opt-level = 2
 debug-assertions = true
 overflow-checks = true
+# This is also set with higher authority in `test_rust.yml`.
 incremental = true