[MINOR] improvement(tez): Only invoking LOG.debug when LOG.isDebugEnabled is true

[rickyma]

What changes were proposed in this pull request?

Only invoking LOG.debug when LOG.isDebugEnabled is true

Why are the changes needed?

For #1201

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Existing UTs.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 55.16%. Comparing base (e043479) to head (0fed8de).

Files	Patch %	Lines
...untime/library/common/sort/buffer/WriteBuffer.java	0.00%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1541      +/-   ##
============================================
+ Coverage     54.19%   55.16%   +0.96%     
  Complexity     2835     2835              
============================================
  Files           436      416      -20     
  Lines         24527    22167    -2360     
  Branches       2075     2076       +1     
============================================
- Hits          13293    12228    -1065     
+ Misses        10406     9181    -1225     
+ Partials        828      758      -70     

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[github-actions]

Test Results

2 452 files  ±0  2 452 suites  ±0   4h 42m 20s ⏱️ -38s
  823 tests ±0    822 ✅ ±0   1 💤 ±0  0 ❌ ±0 
9 743 runs  ±0  9 729 ✅ ±0  14 💤 ±0  0 ❌ ±0 

Results for commit 0fed8de. ± Comparison against base commit e043479.

[jerqi]

LGTM. thanks @rickyma