I wonder if this will do anything?

.github/workflows/main.yml

@@ -40,13 +40,13 @@ jobs:
             cp src/mlpack/bindings/R/mlpack/DESCRIPTION.in DESCRIPTION
             Rscript -e "install.packages('remotes')" -e "saveRDS(remotes::dev_package_deps(dependencies = TRUE), 'depends.Rds')"
 
-#        - name: Cache R packages
-#          if: runner.os != 'Windows' && runner.os != 'macOS'
-#          uses: actions/cache@v1
-#          with:
-#            path: ${{ env.R_LIBS_USER }}
-#            key: ${{ runner.os }}-r-release-${{ hashFiles('depends.Rds') }}
-#            restore-keys: ${{ runner.os }}-r-release-
+        - name: Cache R packages
+          if: runner.os != 'Windows'
+          uses: actions/cache@v1
+          with:
+            path: ${{ env.R_LIBS_USER }}
+            key: ${{ runner.os }}-r-release-${{ hashFiles('depends.Rds') }}
+            restore-keys: ${{ runner.os }}-r-release-
 
         - name: Install Build Dependencies
           run: |
@@ -59,6 +59,7 @@ jobs:
           run: |
             remotes::install_deps(dependencies = TRUE)
             remotes::install_cran("roxygen2")
+            remotes::install_cran("processx")
           shell: Rscript {0}
 
         - name: CMake