README: drop the flavor: full-only caveat on ucrt64

Match the action.yml change of the previous commit: with
`please.sh create-sdk-artifact --architecture=ucrt64` now a working
invocation, all four flavors are viable on the `ucrt64` axis.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

README.md

@@ -62,7 +62,7 @@ Git for Windows SDK comes in variants targeting `x86_64` (AKA "64-bit"), `i686`
 
 Please note that only the `build-installers` and the `full` flavors are available for `i686`.
 
-In addition, the `ucrt64` value selects the UCRT64 variant of `git-sdk-64`. While the [migration from MINGW64 to UCRT64](https://github.com/git-for-windows/git-sdk-64/pull/117) is in progress, this variant lives on a transitional `ucrt64` branch of `git-sdk-64`; once the migration concludes, that branch will replace `main`, at which point `architecture: x86_64` will itself produce a UCRT64 SDK and `ucrt64` becomes a synonym. Until then, this axis runs under `MSYSTEM=UCRT64` with `/ucrt64/bin` on PATH, uses an output directory and cache key that are distinct from `x86_64` so the two variants do not collide on the same runner, and only supports `flavor: full`.
+In addition, the `ucrt64` value selects the UCRT64 variant of `git-sdk-64`. While the [migration from MINGW64 to UCRT64](https://github.com/git-for-windows/git-sdk-64/pull/117) is in progress, this variant lives on a transitional `ucrt64` branch of `git-sdk-64`; once the migration concludes, that branch will replace `main`, at which point `architecture: x86_64` will itself produce a UCRT64 SDK and `ucrt64` becomes a synonym. Until then, this axis runs under `MSYSTEM=UCRT64` with `/ucrt64/bin` on PATH and uses an output directory and cache key that are distinct from `x86_64` so the two variants do not collide on the same runner.
 
 ### Verbosity