BUG: Fix Series.update ExtensionArray issue

[dsaxton]

• closes BUG: Series.update() raises ValueError if dtype="string" #33980
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[jreback]

lgtm. there is a release note conflict. can you merge master and ping on green.

[dsaxton]

@jreback ping

[jreback]

thanks @dsaxton

[simonjayhawkins]

hmm, the tests added here fail when backporting this fix. There have been many refactors of the indexing code since 1.0.3

[simonjayhawkins]

hmm, the tests added here fail when backporting this fix. There have been many refactors of the indexing code since 1.0.3

removing the needs backport label for now.

[jreback]

@simonjayhawkins generally in backport i would do the least possible ones to avoid new issues

[simonjayhawkins]

this PR did fix a regression #34020 (comment)

so was a candidate for backport.

[jreback]

i understand but my point is that we only want backport a very minutes number of tegressions - esp later in a release series