[ci] remove R 3.6 macOS CI jobs (#5859)

.ci/test_r_package.sh

@@ -17,7 +17,7 @@ fi
 R_MAJOR_VERSION=( ${R_VERSION//./ } )
 if [[ "${R_MAJOR_VERSION}" == "3" ]]; then
     export R_MAC_VERSION=3.6.3
-    export R_MAC_PKG_URL=${CRAN_MIRROR}/bin/macosx/R-${R_MAC_VERSION}.pkg
+    export R_MAC_PKG_URL=${CRAN_MIRROR}/bin/macosx/R-${R_MAC_VERSION}.nn.pkg
     export R_LINUX_VERSION="3.6.3-1bionic"
     export R_APT_REPO="bionic-cran35/"
 elif [[ "${R_MAJOR_VERSION}" == "4" ]]; then

.github/workflows/r_package.yml

@@ -63,24 +63,12 @@ jobs:
             r_version: 4.2
             build_type: cmake
             container: 'ubuntu:22.04'
-          - os: macOS-latest
-            task: r-package
-            compiler: gcc
-            r_version: 3.6
-            build_type: cmake
-            container: null
           - os: macOS-latest
             task: r-package
             compiler: gcc
             r_version: 4.2
             build_type: cmake
             container: null
-          - os: macOS-latest
-            task: r-package
-            compiler: clang
-            r_version: 3.6
-            build_type: cmake
-            container: null
           - os: macOS-latest
             task: r-package
             compiler: clang