Berry mark walrus operator as side-effect

[s-hadinger]

Description:

Fix for #18997 found by @sfromis

Now the following is allowed and correctly detected as having a side effect:

var a,b
def f() a := b end

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works with Tasmota core ESP32 V.2.0.10
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass