(fix #5067) Drop Java 8 Targeting

[clairemcginty]

Testing: Checked javac/scalacOptions

% sbt "show javacOptions"
...
[info] 	List(-deprecation, -encoding, UTF-8, -feature, -unchecked, -Wextra-implicit, -Wnumeric-widen, -Wunused, -Xlint:_,-implicit-recursion,-recurse-with-default,-unused,-byname-implicit, -Wconf:cat=scala3-migration:s, -Ybackend-parallelism, 10, -language:_, -release, 11, -Ydelambdafy:inline, -Wconf:cat=deprecation&origin=scala\..*&since>2.12.99:s,cat=unused-imports&origin=scala\.collection\.compat\..*:s,cat=unused-imports&origin=kantan\.codecs\.compat\..*:s,cat=unused-imports&origin=com\.spotify\.scio\.repl\.compat\..*:s,cat=unused:e, -Wmacros:after, -Ymacro-annotations, -Xmacro-settings:show-coder-fallback=true)


% sbt "show scalacOptions"
[info] javacOptions
...
[info] 	List(-encoding, utf8, --release, 11)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.56%. Comparing base (91d4d80) to head (ff48046).
Report is 116 commits behind head on main.

❗ Current head ff48046 differs from pull request most recent head d2fca47. Consider uploading reports for the commit d2fca47 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5203   +/-   ##
=======================================
  Coverage   62.56%   62.56%           
=======================================
  Files         301      301           
  Lines       10807    10807           
  Branches      764      764           
=======================================
  Hits         6761     6761           
  Misses       4046     4046           

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[RustedBones]

Let's also update the README

scio/README.md

Line 36 in 80c6d3c

Download and install the [Java Development Kit (JDK)](https://adoptopenjdk.net/index.html) version 8.