[ci] upgrade R to 4.0.5 in CI (#4158)

* [ci] upgrade R to 4.0.5

* get R 4.0.5 from focal repo

.ci/test_r_package.sh

@@ -33,9 +33,9 @@ if [[ "${R_MAJOR_VERSION}" == "3" ]]; then
     export R_LINUX_VERSION="3.6.3-1bionic"
     export R_APT_REPO="bionic-cran35/"
 elif [[ "${R_MAJOR_VERSION}" == "4" ]]; then
-    export R_MAC_VERSION=4.0.4
-    export R_LINUX_VERSION="4.0.4-1.1804.0"
-    export R_APT_REPO="bionic-cran40/"
+    export R_MAC_VERSION=4.0.5
+    export R_LINUX_VERSION="4.0.5-1.2004.0"
+    export R_APT_REPO="focal-cran40/"
 else
     echo "Unrecognized R version: ${R_VERSION}"
     exit -1

.ci/test_r_package_windows.ps1

@@ -66,7 +66,7 @@ if ($env:R_MAJOR_VERSION -eq "3") {
   $env:RTOOLS_BIN = "$RTOOLS_INSTALL_PATH\usr\bin"
   $env:RTOOLS_MINGW_BIN = "$RTOOLS_INSTALL_PATH\mingw64\bin"
   $env:RTOOLS_EXE_FILE = "rtools40-x86_64.exe"
-  $env:R_WINDOWS_VERSION = "4.0.4"
+  $env:R_WINDOWS_VERSION = "4.0.5"
 } else {
   Write-Output "[ERROR] Unrecognized R version: $env:R_VERSION"
   Check-Output $false