Fix undefined variable in memory_source error message

[KaanKesginLW]

The fallback memory_source(::Any) method references an undefined variable t in its error message. This causes an UndefVarError instead of the intended helpful message when passing an unsupported type to CuTexture.

Before: memory_source(::Any) = error("Unknown texture source $(typeof(t))")
After: memory_source(t::Any) = error("Unknown texture source $(typeof(t))")

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.28%. Comparing base (9eb1085) to head (2c9fd46).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
src/texture.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2990      +/-   ##
==========================================
+ Coverage   89.15%   89.28%   +0.13%     
==========================================
  Files         148      148              
  Lines       12885    12885              
==========================================
+ Hits        11488    11505      +17     
+ Misses       1397     1380      -17     

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[maleadt]

Thanks!