CI: move doc job to workspace level (#1489)

This should fix the error we're encountering in #1487, and at the same
time also check all crates have valid documentation, rather than just
`elliptic-curve` and `signature`.

.github/workflows/elliptic-curve.yml

@@ -89,12 +89,3 @@ jobs:
       - run: cargo test --no-default-features
       - run: cargo test
       - run: cargo test --all-features
-
-  doc:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: stable
-      - run: cargo doc --all-features

.github/workflows/signature.yml

@@ -80,12 +80,3 @@ jobs:
           toolchain: ${{ matrix.rust }}
       - run: cargo test --release
         working-directory: signature_derive
-
-  doc:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: stable
-      - run: cargo doc --all-features

.github/workflows/workspace.yml

@@ -5,13 +5,11 @@ on:
     paths-ignore:
       - '**/README.md'
       - '**/CHANGELOG.md'
-      - .github/**
   push:
     branches: master
     paths-ignore:
       - '**/README.md'
       - '**/CHANGELOG.md'
-      - .github/**
 
 env:
   CARGO_INCREMENTAL: 0
@@ -30,6 +28,15 @@ jobs:
           components: clippy
       - run: cargo clippy --all --all-features --tests -- -D warnings
 
+  doc:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: stable
+      - run: cargo doc --all-features
+
   rustfmt:
     runs-on: ubuntu-latest
     steps: