doc: Move upgrade propagator notes to correct section

[NathanielRN]

Which problem is this PR solving?

The OTel JS 0.26.0 release notes say that the propagator was renamed in 0.26.0 while the README upgrade guidelines says it was done in 0.25.0.

Short description of the changes

It seems like the release notes are correct in this case so this PR fixes that.

Type of change

Please delete options that are not relevant.

• This change requires a documentation update

How Has This Been Tested?

N/A

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

Merging #2579 (e32cc90) into main (0d0b668) will decrease coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2579      +/-   ##
==========================================
- Coverage   93.00%   92.86%   -0.15%     
==========================================
  Files         138      125      -13     
  Lines        5092     4552     -540     
  Branches     1095      972     -123     
==========================================
- Hits         4736     4227     -509     
+ Misses        356      325      -31     

Impacted Files	Coverage Δ
...ackages/opentelemetry-sdk-trace-base/src/Tracer.ts
...y-sdk-trace-base/src/export/ConsoleSpanExporter.ts
...-sdk-trace-base/src/export/InMemorySpanExporter.ts
...try-sdk-trace-base/src/export/NoopSpanProcessor.ts
...dk-trace-base/src/export/BatchSpanProcessorBase.ts
...y-sdk-trace-base/src/export/SimpleSpanProcessor.ts
...ckages/opentelemetry-sdk-trace-base/src/utility.ts
...ackages/opentelemetry-sdk-trace-base/src/config.ts
packages/opentelemetry-sdk-trace-base/src/enums.ts
...ase/src/platform/node/export/BatchSpanProcessor.ts
... and 3 more

[obecny]

lgtm thx for changes