feat: reintroduce codecov reports

uses oidc instead of token

.github/workflows/test.yml

@@ -2,7 +2,7 @@ name: Tests
 
 on:
   push:
-    branches: [ master ]
+    branches: [ master, test-ci ]
   pull_request:
     branches: [ master ]
 
@@ -36,4 +36,16 @@ jobs:
           cargo test --target ${{ matrix.target }} --benches --features=nightly
       - name: Test default features
         run: |
-          cargo test --target ${{ matrix.target }}
+          cargo test --target ${{ matrix.target }}
+  codecov:
+    name: CodeCov Report
+    needs: [ test ]
+    steps:
+    - uses: actions/checkout@main
+    - uses: codecov/codecov-action@v4
+      with:
+        fail_ci_if_error: true # optional (default = false)
+        files: ./coverage1.xml,./coverage2.xml # optional
+        flags: unittests # optional
+        name: codecov-umbrella # optional
+        use_oidc: true