test-build.yml: Add test-docs-build

Try use self hosted linux runner to build html and latexpdf to check for errors.
Trying to use the build artifact didn't seem to work, so just run it on its own.
Upload docs/build folder as artifact to enable review without having to build
locally.  Note: doesn't include verific, so will differ slightly from final
published docs.

.github/workflows/test-build.yml

@@ -179,3 +179,40 @@ jobs:
         shell: bash
         run: |
           make -C docs test -j${{ env.procs }}
+
+  test-docs-build:
+    name: Try build docs
+    runs-on: [self-hosted, linux, x64]
+    needs: [pre_docs_job]
+    if: needs.pre_docs_job.outputs.should_skip != 'true'
+    strategy:
+      matrix:
+        docs-target: [html, latexpdf]
+      fail-fast: false
+    steps:
+      - name: Checkout Yosys
+        uses: actions/checkout@v4
+        with:
+          submodules: true
+
+      - name: Runtime environment
+        run: |
+          echo "procs=$(nproc)" >> $GITHUB_ENV
+
+      - name: Build Yosys
+        run: |
+          make config-clang
+          echo "ENABLE_CCACHE := 1" >> Makefile.conf
+          make -j${{ env.procs }}
+
+      - name: Build docs
+        shell: bash
+        run: |
+          make docs DOC_TARGET=${{ matrix.docs-target }}
+
+      - name: Store docs build artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: docs-build-${{ matrix.docs-target }}
+          path: docs/build/
+          retention-days: 7