Backported: https://github.com/Kitware/CMake/commit/79ce0f434e916684d734e136b92e14f472a9d14a

diff -ur a/Tests/CMakeLists.txt b/Tests/CMakeLists.txt
--- a/Tests/CMakeLists.txt	2022-11-01 08:36:33.000000000 -0500
+++ b/Tests/CMakeLists.txt	2023-02-28 15:24:14.294747915 -0600
@@ -1586,6 +1586,7 @@
     )
   list(APPEND TEST_BUILD_DIRS "${CMake_BINARY_DIR}/Tests/ExternalProject")
   set_tests_properties(ExternalProject PROPERTIES
+    ENVIRONMENT GIT_ALLOW_PROTOCOL=file
     RUN_SERIAL 1
     TIMEOUT ${CMAKE_LONG_TEST_TIMEOUT})
 
@@ -2678,6 +2679,7 @@
         -P "${CMake_BINARY_DIR}/Tests/CTestUpdateGIT.cmake"
         )
       list(APPEND TEST_BUILD_DIRS "${CMake_BINARY_DIR}/Tests/${CTestUpdateGIT_DIR}")
+      set_property(TEST CTest.UpdateGIT PROPERTY ENVIRONMENT GIT_ALLOW_PROTOCOL=file)
     endif()
 
     # Test CTest Update with HG