Replace cargo machete with cargo shear (#8094)

We've had good experiences with `cargo shear` at Rerun

.github/workflows/cargo_machete.yml

@@ -1,19 +0,0 @@
-name: Cargo Machete
-
-on: [push, pull_request]
-
-jobs:
-  cargo-machete:
-    runs-on: ubuntu-latest
-    timeout-minutes: 15
-    steps:
-      - uses: dtolnay/rust-toolchain@stable
-        with:
-          toolchain: 1.92
-      - name: Machete install
-        ## The official cargo-machete action
-        uses: bnjbvr/cargo-machete@v0.9.1
-      - name: Checkout
-        uses: actions/checkout@v4
-      - name: Machete Check
-        run: cargo machete

.github/workflows/cargo_shear.yml

@@ -0,0 +1,25 @@
+# Looks for unused crates.
+name: Cargo Shear
+
+on:
+  push:
+    branches:
+      - "main"
+  pull_request:
+    types: [opened, synchronize]
+
+jobs:
+  cargo-shear:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install Cargo Shear
+        uses: taiki-e/install-action@v2.48.7
+        with:
+          tool: cargo-shear@1.11.2
+
+      - name: Run Cargo Shear
+        run: |
+          cargo shear