Add espidf build to CI

Signed-off-by: Joe Richey <[email protected]>

Author: josephlr

.github/workflows/tests.yml

@@ -319,6 +319,8 @@ jobs:
         run: cargo build -Z build-std=core --target=aarch64-kmc-solid_asp3
       - name: Nintendo 3DS
         run: cargo build -Z build-std=core --target=armv6k-nintendo-3ds
+      - name: RISC-V ESP-IDF
+        run: cargo build -Z build-std=core --target=riscv32imc-esp-espidf
       - name: OpenBSD
         run: cargo build -Z build-std=std --target=x86_64-unknown-openbsd --features=std
       - name: Dragonfly BSD