ci: Limit PR builds to 20min

Most runs conclude on the order 5min +/- 2min, so if we hit the 20min
mark chances are something has hung.

Author: alcarney

.github/workflows/lsp-pr.yml

@@ -42,6 +42,7 @@ jobs:
   test:
     name: "Python v${{ matrix.python-version }} -- ${{ matrix.os }}"
     runs-on: ${{ matrix.os }}
+    timeout-minutes: 20
     strategy:
       fail-fast: false
       matrix: