ci: 👷 split into main vs PR build CI workflows (#174)

## Description

These changes are made because the styling and documenting can only be
done on non-main branches. So this adds two builds.

.github/workflows/build-pr.yaml

@@ -0,0 +1,39 @@
+# Workflow derived from https://github.com/r-lib/actions/tree/v2/examples
+# Need help debugging build failures? Start at https://github.com/r-lib/actions#where-to-find-help
+on:
+  pull_request:
+    branches: main
+
+name: Build package
+
+permissions: read-all
+
+jobs:
+  style:
+    uses: ./.github/workflows/reusable-style.yaml
+    permissions:
+      contents: write
+    secrets:
+      github-token: ${{ secrets.GITHUB_TOKEN }}
+
+  document:
+    uses: ./.github/workflows/reusable-document.yaml
+    needs: style
+    permissions:
+      contents: write
+    secrets:
+      github-token: ${{ secrets.GITHUB_TOKEN }}
+
+  cran-check:
+    uses: ./.github/workflows/reusable-cran-check.yaml
+    needs: document
+    secrets:
+      github-token: ${{ secrets.GITHUB_TOKEN }}
+
+  pkgdown:
+    uses: ./.github/workflows/reusable-pkgdown.yaml
+    needs: cran-check
+    permissions:
+      contents: write
+    secrets:
+      github-token: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/build.yaml

@@ -3,8 +3,6 @@
 on:
   push:
     branches: main
-  pull_request:
-    branches: main
   release:
     types: [published]
 
@@ -13,24 +11,8 @@ name: Build package
 permissions: read-all
 
 jobs:
-  style:
-    uses: ./.github/workflows/reusable-style.yaml
-    permissions:
-      contents: write
-    secrets:
-      github-token: ${{ secrets.GITHUB_TOKEN }}
-
-  document:
-    uses: ./.github/workflows/reusable-document.yaml
-    needs: style
-    permissions:
-      contents: write
-    secrets:
-      github-token: ${{ secrets.GITHUB_TOKEN }}
-
   cran-check:
     uses: ./.github/workflows/reusable-cran-check.yaml
-    needs: document
     secrets:
       github-token: ${{ secrets.GITHUB_TOKEN }}