Replace non-breaking space characters in code snippets

Some of the sketch code was littered with random use of the non-breaking space character in place of standard space characters. Although the two characters appear the same to a human, they are not the same to the compiler, and so cause spurious errors when the sketch was compiled:

```
sketch_nov15a.ino:3:1: error: stray '\302' in program
     // initialize digital pin LEDR as an output.
 ^
sketch_nov15a.ino:3:2: error: stray '\240' in program
     // initialize digital pin LEDR as an output.
  ^

exit status 1

Compilation error: stray '\302' in program
```

The solution is to replace these invalid characters with standard spaces

Author: per1234

content/hardware/04.pro/boards/portenta-h7/tutorials/dual-core-processing/content.md

@@ -64,15 +64,15 @@ The following sketch blinks the red LED at an interval of 200ms controlled by th
 ```cpp
 // the setup function runs once when you press reset or power the board
 void setup() {
-    // initialize digital pin LEDR as an output.
+    // initialize digital pin LEDR as an output.
     pinMode(LEDR, OUTPUT);
 }
 
 // the loop function runs over and over again forever
 void loop() {
    digitalWrite(LEDR, LOW); // turn the red LED on (LOW is the voltage level)
    delay(200); // wait for 200 milliseconds
-   digitalWrite(LEDR, HIGH); // turn the LED off by making the voltage HIGH
+   digitalWrite(LEDR, HIGH); // turn the LED off by making the voltage HIGH
    delay(200); // wait for 200 milliseconds
 }
 ```
@@ -88,15 +88,15 @@ Let's write another sketch that makes the RGB LED on the board blink green. Open
 ```cpp
 // the setup function runs once when you press reset or power the board
 void setup() {
-    // initialize digital pin LEDG as an output.
+    // initialize digital pin LEDG as an output.
     pinMode(LEDG, OUTPUT);
 }
 
 // the loop function runs over and over again forever
 void loop() {
    digitalWrite(LEDG, LOW); // turn the LED on (LOW is the voltage level)
    delay(500); // wait for half a second
-   digitalWrite(LEDG, HIGH); // turn the LED off by making the voltage HIGH
+   digitalWrite(LEDG, HIGH); // turn the LED off by making the voltage HIGH
    delay(500); // wait for half a second
 }
 ```
@@ -113,7 +113,7 @@ Before you can upload the code for the M4 core to the Flash memory you need to a
 ```cpp
 // the setup function runs once when you press reset or power the board
 void setup() {
-    // initialize digital pin LED_BUILTIN as an output.
+    // initialize digital pin LED_BUILTIN as an output.
    bootM4();
    pinMode(LEDR, OUTPUT);
 }