PageCoroutine checks

[elacuesta]

• Warn (and skip) if a value in playwright_page_coroutines is not a PageCoroutine object
• Also accept non-awaitable calls (not strictly only coroutines anymore but hey, why not?)

[codecov]

Codecov Report

Merging #69 (bcef5ef) into master (7e678ce) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #69   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          252       257    +5     
=========================================
+ Hits           252       257    +5     

Impacted Files	Coverage Δ
scrapy_playwright/handler.py	100.00% <100.00%> (ø)

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