[R-package] [ci] add correct path for mingw32-make in CI (#3523)

.ci/test_r_package_windows.ps1

@@ -51,7 +51,7 @@ if ($env:R_MAJOR_VERSION -eq "3") {
 
 $env:R_LIB_PATH = "$env:BUILD_SOURCESDIRECTORY/RLibrary" -replace '[\\]', '/'
 $env:R_LIBS = "$env:R_LIB_PATH"
-$env:PATH = "$RTOOLS_INSTALL_PATH/bin;" + "$RTOOLS_INSTALL_PATH/usr/bin;" + "$env:R_LIB_PATH/R/bin/x64;" + "$env:R_LIB_PATH/miktex/texmfs/install/miktex/bin/x64;" + $env:PATH
+$env:PATH = "$RTOOLS_INSTALL_PATH/bin;" + "$RTOOLS_INSTALL_PATH/usr/bin;" + "$env:RTOOLS_MINGW_BIN;" + "$env:R_LIB_PATH/R/bin/x64;" + "$env:R_LIB_PATH/miktex/texmfs/install/miktex/bin/x64;" + $env:PATH
 $env:CRAN_MIRROR = "https://cloud.r-project.org/"
 $env:CTAN_MIRROR = "https://ctan.math.illinois.edu/systems/win32/miktex"
 $env:CTAN_PACKAGE_ARCHIVE = "$env:CTAN_MIRROR/tm/packages/"