Add (and fix) i2c-passthru example with CI

Author: jamesmunns

ci.sh

@@ -79,3 +79,24 @@ cargo build \
 cargo build \
     --manifest-path examples/waveshare-rp2040-keyboard-3/demo/Cargo.toml \
     --profile ci
+
+### i2c-passthru
+cargo check \
+    --manifest-path examples/i2c-passthru/icd/Cargo.toml \
+    --features="use-std" \
+    --profile ci
+
+cargo check \
+    --manifest-path examples/i2c-passthru/icd/Cargo.toml \
+    --no-default-features \
+    --target thumbv6m-none-eabi \
+    --profile ci
+
+cargo build \
+    --manifest-path examples/i2c-passthru/rp2040/Cargo.toml \
+    --target thumbv6m-none-eabi \
+    --profile ci
+
+cargo build \
+    --manifest-path examples/i2c-passthru/demo/Cargo.toml \
+    --profile ci

examples/i2c-passthru/icd/Cargo.toml

@@ -16,7 +16,7 @@ version = "0.2"
 features = ["derive"]
 
 [features]
-use-std = []
+use-std = ["postcard-schema/use-std"]
 
 [profile.ci]
 inherits = "dev"