ci: Change Makevars only after installation of R

.github/workflows/R-CMD-check.yaml

@@ -108,14 +108,15 @@ jobs:
           # Beware of using dev pkgdown here, has brought in dev dependencies in the past
           extra-packages: any::rcmdcheck r-lib/roxygen2 any::decor r-lib/styler r-lib/pkgdown deps::.
 
+      - uses: ./.github/workflows/custom/after-install
+        if: hashFiles('.github/workflows/custom/after-install/action.yml') != ''
+
+      # Must come after the custom after-install workflow
       - name: Install package
         run: |
           _R_SHLIB_STRIP_=true R CMD INSTALL .
         shell: bash
 
-      - uses: ./.github/workflows/custom/after-install
-        if: hashFiles('.github/workflows/custom/after-install/action.yml') != ''
-
       - id: versions-matrix
         # Only run for pull requests if the base repo is different from the head repo, not for workflow_dispatch if not requested, always run for other events
         if: (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.repository) && (github.event_name != 'workflow_dispatch' || inputs.versions-matrix)

.github/workflows/custom/after-install/action.yml

@@ -0,0 +1,10 @@
+name: 'Custom steps to run after R packages are installed'
+
+runs:
+  using: "composite"
+  steps:
+    - name: Use GLPK on macOS
+      if: runner.os == 'macOS'
+      run: |
+        echo -e 'CPPFLAGS = -I/opt/homebrew/include\nLDFLAGS = -L/opt/homebrew/lib' | tee ~/.R/Makevars
+      shell: bash

.github/workflows/custom/before-install/action.yml

@@ -8,9 +8,8 @@ runs:
         echo '_R_CHECK_PKG_SIZES_=FALSE' | tee -a $GITHUB_ENV
       shell: bash
 
-    - name: Install and use GLPK on macOS
+    - name: Install GLPK on macOS
       if: runner.os == 'macOS'
       run: |
         brew install glpk
-        echo -e 'CPPFLAGS = -I/opt/homebrew/include\nLDFLAGS = -L/opt/homebrew/lib' | tee ~/.R/Makevars
       shell: bash