[NFC][clangd][test] add clang-tidy config to ensure test cases sandbox

Under previous test setup, the test result will be influenced by clang-tidy file in parent folder (between llvm-projects root and build folder). It is inconventient and leads some confusion.
This PR wants to ensure sandbox to avoid outside's clang-tidy influenece test result.

Author: HerrCai0907

clang-tools-extra/clangd/test/Inputs/path-mappings/server/.clang-tidy

@@ -0,0 +1 @@
+InheritParentConfig: false

clang-tools-extra/clangd/test/system-include-extractor.test

@@ -32,6 +32,9 @@
 # RUN: echo 'printf "End of search list.\r\n" >&2' >> %t.dir/bin/my_driver.sh
 # RUN: chmod +x %t.dir/bin/my_driver.sh
 
+# Create fake clang-tidy config to ensure sandbox
+# RUN: echo 'InheritParentConfig: false' >> %t.dir/.clang-tidy
+
 # Create header files my/dir/a.h and my/dir2/b.h
 # RUN: mkdir -p %t.dir/my/dir
 # RUN: touch %t.dir/my/dir/a.h