CI: Enable code coverage again.

.github/workflows/coverage.yml

@@ -0,0 +1,36 @@
+name: Code coverage
+
+on:
+  push:
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  code_coverage:
+  name: Code Coverage
+  runs-on: "ubuntu-latest"
+  steps:
+    - name: Checkout repository
+      uses: actions/checkout@v2
+
+    - name: Install stable toolchain
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: stable
+        override: true
+
+    - name: Install tarpaulin
+      uses: actions-rs/cargo@v1
+      with:
+        command: install
+        args: cargo-tarpaulin -f
+
+    - name: Run tarpaulin
+      uses: actions-rs/cargo@v1
+      with:
+        command: tarpaulin
+        args: --ignore-config --exclude-files "matrix_sdk/examples/*,matrix_sdk_common,matrix_sdk_test" --out Xml
+
+    - name: Upload to codecov.io
+      uses: codecov/codecov-action@v1