Fix issues found by JET

[odow]

Following up to #4148

julia> JET.report_package(JuMP; target_modules=(JuMP,))
[toplevel-info] Analyzing top-level definitions (progress: 2012/2012)
[toplevel-info] Analyzed all top-level definitions (all: 2012 | analyzed: 8 | cached: 2004 | took: 0.019 sec)
No errors detected

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.91%. Comparing base (0fda642) to head (3c64837).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4149   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files          42       42           
  Lines        6223     6224    +1     
=======================================
+ Hits         6218     6219    +1     
  Misses          5        5           

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