Merge branch 'es/shell-check-updates'

Merge branch 'es/shell-check-updates'

Test script linter has been updated to catch an attempt to use
one-shot export construct "VAR=VAL func" for shell functions (which
does not work for some shells) better.

* es/shell-check-updates:
  check-non-portable-shell: improve `VAR=val shell-func` detection
  check-non-portable-shell: suggest alternative for `VAR=val shell-func`
  check-non-portable-shell: loosen one-shot assignment error message
  t4034: fix use of one-shot variable assignment with shell function
  t3430: drop unnecessary one-shot "VAR=val shell-func" invocation