[chore](trx-rs): install libclang for soapysdr-sys in CI

soapysdr-sys builds bindings with bindgen, which needs libclang at build
time. Add clang and libclang-dev to the system dependencies so the
soapysdr backend (a default feature) compiles under CI.

Assisted-By: Claude Code (claude-opus-4)
Claude-Session: https://claude.ai/code/session_01NFpGtGTWUEYXLwZeZs2RAV
Signed-off-by: Stan Grams <sjg@haxx.space>

.gitea/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y --no-install-recommends \
-            build-essential pkg-config cmake \
+            build-essential pkg-config cmake clang libclang-dev \
             libopus-dev libasound2-dev libsoapysdr-dev
 
       - name: Set up Rust
@@ -65,7 +65,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y --no-install-recommends \
-            build-essential pkg-config cmake \
+            build-essential pkg-config cmake clang libclang-dev \
             libopus-dev libasound2-dev libsoapysdr-dev
 
       - name: Set up Rust