Fix CI pipeline - check major versions only for commands

[alexole]

About this change - What it does

Fixes the CI pipeline

Why this way

In the tests we check the full versions of the PG binaries used, some packages are shipped with different minor versions of binaries (not necessarily the latest), so we should check major version only, they should be compatible.

[rdunklau]

Now that we don't test against 9.6 anymore, this looks like a good idea.

[codecov]

Codecov Report

Merging #534 (292dc52) into main (af2a914) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #534      +/-   ##
==========================================
+ Coverage   89.39%   89.42%   +0.02%     
==========================================
  Files          29       29              
  Lines        4490     4490              
==========================================
+ Hits         4014     4015       +1     
+ Misses        476      475       -1     

Impacted Files	Coverage Δ
pghoard/pghoard.py	82.79% <0.00%> (+0.16%)	⬆️

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