CI - clang-format-18 (#9225)

* Fix shell variable comparison without $CI present

+ '[' = true ']'
./tests/restyle.sh: line 16: [: =: unary operator expected

vs.

+ '[' '' = true ']'

* Update to clang-format-18

new opt to skip overly eager macro formatting
https://clang.llvm.org/docs/ClangFormatStyleOptions.html#skipmacrodefinitionbody

minor changes between 15 and 18 for ide examples

reference arduino-ide format is still stuck with 15, though
https://github.com/arduino/clang-static-binaries/releases

* Pin clang-format in CI recipe not the script itself

* style

libraries/ESP8266WebServer/examples/WebServer/WebServer.ino

@@ -153,7 +153,7 @@ public:
       // Close the file
       if (_fsUploadFile) { _fsUploadFile.close(); }
     }  // if
-  }    // upload()
+  }  // upload()
 
 protected:
   File _fsUploadFile;