cmd/warmup: fix handling of relative paths

[SandyXSD]

No description provided.

[codecov-commenter]

Codecov Report

Merging #1735 (d6af337) into main (074f538) will increase coverage by 0.03%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##             main    #1735      +/-   ##
==========================================
+ Coverage   61.85%   61.89%   +0.03%     
==========================================
  Files         135      135              
  Lines       22899    22905       +6     
==========================================
+ Hits        14165    14176      +11     
+ Misses       7142     7139       -3     
+ Partials     1592     1590       -2     

Impacted Files	Coverage Δ
cmd/warmup.go	63.56% <42.85%> (-0.67%)	⬇️
pkg/chunk/utils_unix.go	73.33% <0.00%> (-20.00%)	⬇️
pkg/meta/sql.go	67.33% <0.00%> (+0.20%)	⬆️
pkg/chunk/cached_store.go	80.40% <0.00%> (+1.29%)	⬆️

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