ci: update vcpkg url regex (#15998)

Author: scotthart

ci/kokoro/lib/vcpkg.sh

@@ -32,7 +32,7 @@ install_vcpkg() {
   io::log "Downloading vcpkg into ${vcpkg_dir}..."
   VCPKG_VERSION="$(<ci/etc/vcpkg-version.txt)"
   url="https://github.com/microsoft/vcpkg/archive/${VCPKG_VERSION}.tar.gz"
-  if [[ "${VCPKG_VERSION}" =~ [0-9]{4}.[0-9]{2}.[0-9]{2} ]]; then
+  if [[ "${VCPKG_VERSION}" =~ [0-9]{4}\.[0-9]{2}\.[0-9]{2} ]]; then
     # vcpkg uses date-like tags for releases
     url="https://github.com/microsoft/vcpkg/archive/refs/tags/${VCPKG_VERSION}.tar.gz"
   fi

ci/kokoro/windows/lib/vcpkg.ps1

@@ -69,7 +69,7 @@ function Install-Vcpkg {
 
     $vcpkg_version = Get-Content -Path "${project_root}\ci\etc\vcpkg-version.txt"
     $vcpkg_url = "https://github.com/microsoft/vcpkg/archive/${vcpkg_version}.zip"
-    if ($vcpkg_version -match "[0-9]{4}.[0-9]{2}.[0-9]{2}" ) {
+    if ($vcpkg_version -match "[0-9]{4}\.[0-9]{2}\.[0-9]{2}" ) {
         $vcpkg_url = "https://github.com/microsoft/vcpkg/archive/refs/tags/${vcpkg_version}.zip"
     }
     Write-Host "$(Get-Date -Format o) Downloading vcpkg archive from $vcpkg_url"