fix(IWatchdog): remove errors and warnings raised by arduino-lint

ERROR: library.properties url value is less than minimum length. (Rule LP056)
ERROR: library.properties url field value  does not have a valid URL format. (Rule LP041)
WARNING: Unable to load the library.properties url field: Head "": unsupported protocol scheme "" (Rule LP042)

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

libraries/IWatchdog/library.properties

@@ -5,5 +5,5 @@ maintainer=stm32duino
 sentence=Enables support for independent watchdog (IWDG) hardware on STM32 processors.
 paragraph=Independent watchdog (IWDG) is a hardware timer on the chip which would generate a reset condition if the time is not reloaded within the specified time. It is generally used in production systems to reset the system if the CPU becomes "stuck".
 category=Timing
-url=
+url=https://github.com/stm32duino/Arduino_Core_STM32/blob/main/libraries/IWatchdog/README.md
 architectures=stm32