For code doing it wrong, ensure priority is set

[mikejolley]

If someone is adding tabs but not setting priority, this avoids a notice.

[codecov]

Codecov Report

Merging #17521 into master will not change coverage.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master   #17521   +/-   ##
=========================================
  Coverage     35.09%   35.09%           
  Complexity    12147    12147           
=========================================
  Files           325      325           
  Lines         49706    49706           
=========================================
  Hits          17442    17442           
  Misses        32264    32264

Impacted Files	Coverage Δ	Complexity Δ
includes/wc-template-functions.php	0.78% <0%> (ø)	0 <0> (ø)	⬇️

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