ci: workaround RUSTFLAGS leaking into cargo-make rust-script builds

Unset RUSTFLAGS for the cargo-make step in build.yaml to prevent -D warnings
from leaking into rust-script compilation of wdk-build. Only cargo-make is
affected since it uses rust-script to compile inline build scripts where
wdk-build is a path dependency (via symlink), bypassing cargo's --cap-lints.
cargo-wdk and cargo install are normal cargo operations with proper
--cap-lints handling and do not need this workaround.

Temporary workaround until microsoft/windows-drivers-rs#629 is merged and
a new wdk-build is published.

Tracked in ADO Bug #5396440.

Author: wmmc88

.github/workflows/build.yaml

@@ -107,7 +107,13 @@ jobs:
           tool: cargo-make
 
       - name: Build and Package Sample Drivers
-        run: cargo make default +${{ matrix.rust_toolchain }} --locked --profile ${{ matrix.cargo_profile }} --target ${{ matrix.target_triple.name }}
+        # Unset RUSTFLAGS for cargo-make to work around RUSTFLAGS leaking into
+        # rust-script compilation of wdk-build (path dep via symlink defeats
+        # --cap-lints). Upstream fix: microsoft/windows-drivers-rs#629
+        run: |
+          $env:RUSTFLAGS = $null
+          cargo make default +${{ matrix.rust_toolchain }} --locked --profile ${{ matrix.cargo_profile }} --target ${{ matrix.target_triple.name }}
+        shell: pwsh
 
       # Steps to use cargo-wdk to build and package drivers
       - name: Install cargo-wdk binary