Check R-devel on Windows in CI (#141)

* Check R-devel on Windows in CI

Adds a windows-latest / R-devel entry to the R CMD check matrix,
providing the coverage previously obtained by manual win-builder
(devtools::check_win_devel()) uploads on every push instead.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Also check R-devel on macOS

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: bocinsky

.github/workflows/check-standard.yaml

@@ -19,7 +19,9 @@ jobs:
       matrix:
         config:
           - {os: macos-latest,   r: 'release'}
+          - {os: macos-latest,   r: 'devel'}
           - {os: windows-latest, r: 'release'}
+          - {os: windows-latest, r: 'devel'}
           - {os: ubuntu-latest,   r: 'devel', http-user-agent: 'release'}
           - {os: ubuntu-latest,   r: 'release'}
           - {os: ubuntu-latest,   r: 'oldrel-1'}