Fix wrong variable name in import expression

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:
Resolves #3072

Description

Import expressions did not properly render their source, which meant that variable name changes could be lost.

[codecov]

Codecov Report

Merging #3073 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3073      +/-   ##
==========================================
+ Coverage    88.8%   88.81%   +<.01%     
==========================================
  Files         165      165              
  Lines        5728     5729       +1     
  Branches     1743     1743              
==========================================
+ Hits         5087     5088       +1     
  Misses        388      388              
  Partials      253      253

Impacted Files	Coverage Δ
src/ast/nodes/ImportExpression.ts	100% <100%> (ø)	⬆️

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