gh-actions: setup R with r-lib/actions also on linux

rpy2 does not seem to find R packages otherwise

Change-Id: Iec4c1cdad990825ee3ab44e51d0b1330158305b4
diff --git a/.github/workflows/pythonpackage.yml b/.github/workflows/pythonpackage.yml
index 6eba34c..0dc1ba5 100644
--- a/.github/workflows/pythonpackage.yml
+++ b/.github/workflows/pythonpackage.yml
@@ -7,6 +7,7 @@
 
     runs-on: ${{ matrix.os }}
     strategy:
+      max-parallel: 4
       fail-fast: false
       matrix:
         python-version: [3.7, 3.8]
@@ -43,14 +44,14 @@
       uses: r-lib/actions/setup-r@master
       with:
         r-version: ${{ matrix.r-version }}
-      if: runner.os != 'Linux'
+      if: runner.os != 'LinuxDisabled'
     - name: Set up package maintainers R on Linux
       run: |
         sudo apt-get update -y
         sudo apt-get install -y r-base r-base-dev r-cran-tidyverse r-cran-r.utils r-cran-pixmap r-cran-webshot r-cran-ade4 r-cran-segmented r-cran-purrr r-cran-dygraphs r-cran-cvst r-cran-quantmod r-cran-graphlayouts r-cran-rappdirs r-cran-ggdendro r-cran-seqinr r-cran-heatmaply r-cran-igraph r-cran-plotly libcurl4-gnutls-dev libssl-dev libxml2-dev libsodium-dev python3-pip python3-rpy2 python3-pandas
         sudo chown $USER /usr/local/lib/R/site-library
         export R_LIBS_USER=/usr/local/lib/R/site-library
-      if: runner.os == 'Linux'
+      if: runner.os == 'LinuxDisabled'
     - name: Install R dependencies
       run: Rscript -e "install.packages('RKorAPClient')"
     - name: Cache R packages on Linux