Tests: Fix RunCMake.ExternalProject when git is not available

Move Git-dependent test cases added by commit 2ef3bd9186
(ExternalProject: Add TLS version options for https connections,
2024-02-26, v3.30.0-rc1~471^2) into the block of cases that run only
when Git is found.

Fixes: #26104

Tests/RunCMake/ExternalProject/RunCMakeTest.cmake

@@ -15,9 +15,6 @@ endif()
 
 run_cmake(BadIndependentStep1)
 run_cmake(BadIndependentStep2)
-run_cmake(TLSVersionBadArg)
-run_cmake(TLSVersionBadVar)
-run_cmake(TLSVersionBadEnv)
 run_cmake(NoOptions)
 run_cmake(SourceEmpty)
 run_cmake(SourceMissing)
@@ -256,5 +253,9 @@ if(GIT_EXECUTABLE)
   # on some platforms. It may go to stdout or stderr, so force it to be merged.
   set(RunCMake_TEST_OUTPUT_MERGE TRUE)
   run_cmake(FetchGitRefs)
-  set(RunCMake_TEST_OUTPUT_MERGE FALSE)
+  unset(RunCMake_TEST_OUTPUT_MERGE)
+
+  run_cmake(TLSVersionBadArg)
+  run_cmake(TLSVersionBadVar)
+  run_cmake(TLSVersionBadEnv)
 endif()