Bump version to v1.38.0-pre1 (grpc#26208)

* Bump version to v1.38.0-pre1

* Regenerate projects

Bump to 1.37.1 (grpc#26040)

* Bump to 1.37.1

* Regenerate projects

Bump to 1.37.0 for Final Release (grpc#25891)

* Bump version to 1.37.0

* Regenerate projects

Bump to 1.37.0-pre1 (grpc#25839)

* Bump to v1.37.0-pre1

* Regenerate projects

Bump version to 1.36.4 (grpc#25744)

Fix an infinite read loop with SRV record resolution on windows (grpc…

…#25690)

[Backport] Update the way dockerfiles install pip for python 2.7 and …

…3.5 (grpc#25607)

* Backport: Update the way dockerfiles install pip for python 2.7 and 3.5

* Fix implicit-int-float-conversion warning.

Co-authored-by: Jan Tattermusch <[email protected]>
Co-authored-by: Levon Ter-Grigoryan <[email protected]>

Relax ruby test check on protobuf error message (grpc#25507) (grpc#25591

)

Co-authored-by: apolcyn <[email protected]>

Bump version to v1.36.0 (grpc#25534)

Merge pull request grpc#25433 from jtattermusch/backport_25420

Backport grpc#25420 into v1.36.x