fix(ci): Do not run coverage in merge queue (#239)

## Overview

Changes the codecov job to not run in the merge queue.

See: matplotlib/napari-matplotlib#155

.github/workflows/coverage.yaml

@@ -0,0 +1,41 @@
+name: Rust Coverage
+on:
+  push:
+    branches: [main]
+  pull_request:
+env:
+  CARGO_TERM_COLOR: always
+jobs:
+  coverage:
+    runs-on: ubuntu-latest
+    name: codecov
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
+      - name: Install stable
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: llvm-tools-preview
+      - name: Rust cache
+        uses: Swatinem/rust-cache@v2
+        with:
+          cache-on-failure: true
+      - name: cargo install cargo-llvm-cov
+        uses: taiki-e/install-action@cargo-llvm-cov
+      - name: cargo install cargo-nextest
+        uses: taiki-e/install-action@nextest
+      - name: cargo generate-lockfile
+        if: hashFiles('Cargo.lock') == ''
+        run: cargo generate-lockfile
+      - name: cargo llvm-cov
+        run: cargo llvm-cov nextest --locked --workspace --lcov --output-path lcov.info
+      - name: Record Rust version
+        run: echo "RUST=$(rustc --version)" >> "$GITHUB_ENV"
+      - name: Upload to codecov.io
+        uses: codecov/codecov-action@v4
+        with:
+          fail_ci_if_error: true
+          token: ${{ secrets.CODECOV_TOKEN }}
+          env_vars: OS,RUST
+          files: lcov.info

.github/workflows/rust_ci.yaml

@@ -96,36 +96,3 @@ jobs:
         run: just lint-docs
       - name: doctest
         run: just test-docs
-  coverage:
-    runs-on: ubuntu-latest
-    name: codecov
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          submodules: true
-      - name: Install stable
-        uses: dtolnay/rust-toolchain@stable
-        with:
-          components: llvm-tools-preview
-      - name: Rust cache
-        uses: Swatinem/rust-cache@v2
-        with:
-          cache-on-failure: true
-      - name: cargo install cargo-llvm-cov
-        uses: taiki-e/install-action@cargo-llvm-cov
-      - name: cargo install cargo-nextest
-        uses: taiki-e/install-action@nextest
-      - name: cargo generate-lockfile
-        if: hashFiles('Cargo.lock') == ''
-        run: cargo generate-lockfile
-      - name: cargo llvm-cov
-        run: cargo llvm-cov nextest --locked --workspace --lcov --output-path lcov.info
-      - name: Record Rust version
-        run: echo "RUST=$(rustc --version)" >> "$GITHUB_ENV"
-      - name: Upload to codecov.io
-        uses: codecov/codecov-action@v4
-        with:
-          fail_ci_if_error: true
-          token: ${{ secrets.CODECOV_TOKEN }}
-          env_vars: OS,RUST
-          files: lcov.info