Be more robust to failed `julia -v` commands

[LilithHafner]

From https://discourse.julialang.org/t/updatejulia/72128/12?u=lilith

[codecov-commenter]

Codecov Report

Merging #20 (b571696) into main (ffe1e0c) will decrease coverage by 8.37%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
- Coverage   86.48%   78.10%   -8.38%     
==========================================
  Files           1        1              
  Lines         185      169      -16     
==========================================
- Hits          160      132      -28     
- Misses         25       37      +12     

Impacted Files	Coverage Δ
src/UpdateJulia.jl	78.10% <100.00%> (-8.38%)	:arrow_down:

:mega: We’re building smart automated test selection to slash your CI/CD build times. Learn more