Lower JVM toolchain down to 8

[twyatt]

With #261, the JDK version used on CI was bumped up to 17 for compatibility with Android Gradle plugin (AGP) 8.0+; but the source and target compatibilities were also bumped in that PR.

This PR reverts the source and target compatibilities bumps so that library consumers aren't forced to bump their JDK versions (if they're still on JDK 8).

[codecov]

Codecov Report

Merging #268 (c085c4c) into main (1c1547e) will decrease coverage by 8.99%.
The diff coverage is 80.27%.

❗ Current head c085c4c differs from pull request most recent head 0c43b40. Consider uploading reports for the commit 0c43b40 to get more accurate results

@@             Coverage Diff              @@
##               main     #268      +/-   ##
============================================
- Coverage     94.44%   85.46%   -8.99%     
- Complexity       51       91      +40     
============================================
  Files            13       20       +7     
  Lines           126      282     +156     
  Branches          8       15       +7     
============================================
+ Hits            119      241     +122     
- Misses            6       37      +31     
- Partials          1        4       +3     

Impacted Files	Coverage Δ
coroutines/src/commonMain/kotlin/flow/Combine.kt	0.00% <ø> (ø)
logging/src/commonMain/kotlin/Metadata.kt	76.92% <0.00%> (-0.86%)	⬇️
logging/src/commonMain/kotlin/Sensitivity.kt	0.00% <0.00%> (ø)
...tines/src/commonMain/kotlin/delay/DelayStrategy.kt	47.50% <47.50%> (ø)
logging/src/commonMain/kotlin/DispatchLogger.kt	92.10% <89.65%> (-7.90%)	⬇️
logging/src/commonMain/kotlin/Log.kt	98.27% <93.75%> (-1.73%)	⬇️
logging/src/commonMain/kotlin/FilterLogger.kt	95.65% <95.65%> (ø)
...t/src/commonMain/kotlin/TuulboxKtorClientLogger.kt	100.00% <100.00%> (ø)
logging/src/commonMain/kotlin/FilterLevelLogger.kt	100.00% <100.00%> (ø)
logging/src/commonMain/kotlin/LogLevel.kt	100.00% <100.00%> (ø)
... and 1 more

... and 2 files with indirect coverage changes

[github-actions]

Test Results

  32 files    32 suites   7s ⏱️
233 tests 226 ✔️   7 💤 0 ❌
250 runs  238 ✔️ 12 💤 0 ❌

Results for commit 0c43b40.

♻️ This comment has been updated with latest results.