Fix command execution in pr-validation

[svenklemm]

The github action to check for multiple commits would check the
pullrequest message for a command to disable the check.
While processing the message any commands enclosed in backticks
would be executed as shell commands.

[codecov]

Codecov Report

Merging #3100 (4cd9e88) into master (31e1a9c) will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3100      +/-   ##
==========================================
+ Coverage   90.20%   90.29%   +0.09%     
==========================================
  Files         215      215              
  Lines       35299    35249      -50     
==========================================
- Hits        31841    31829      -12     
+ Misses       3458     3420      -38     

Impacted Files	Coverage Δ
src/loader/bgw_message_queue.c	84.51% <0.00%> (-2.59%)	⬇️
src/loader/bgw_launcher.c	89.50% <0.00%> (-2.47%)	⬇️
tsl/src/data_node_dispatch.c	97.07% <0.00%> (-0.25%)	⬇️
tsl/src/reorder.c	82.10% <0.00%> (+0.26%)	⬆️
src/import/planner.c	70.30% <0.00%> (+11.12%)	⬆️

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