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/I2S/examples/InputSerialPlotter/InputSerialPlotter.ino

@@ -21,8 +21,7 @@ void setup() {
   // start I2S at 8 kHz with 24-bits per sample
   if (!I2S.begin(I2S_PHILIPS_MODE, 8000, 24)) {
     Serial.println("Failed to initialize I2S!");
-    while (1)
-      ;  // do nothing
+    while (1);  // do nothing
   }
 }
 

libraries/I2S/examples/SimpleTone/SimpleTone.ino

@@ -26,8 +26,7 @@ void setup() {
   // start I2S at the sample rate with 16-bits per sample
   if (!I2S.begin(I2S_PHILIPS_MODE, sampleRate, 16)) {
     Serial.println("Failed to initialize I2S!");
-    while (1)
-      ;  // do nothing
+    while (1);  // do nothing
   }
 }