CI: Rename Windows installer artifacts to dmd-<branch>.exe

Don't use the DMD VERSION file, currently leading to names like
`dmd-v2.110.0-beta.1.exe`, which accumulate for the nightly release:
https://github.com/dlang/dmd/releases/tag/nightly

Switch to `dmd-master.exe`, similar to the other artifact names.

.github/workflows/build_release_template.yml

@@ -252,6 +252,7 @@ jobs:
           for /f %%v in (dmd.windows\dmd2\src\VERSION) do set ver=%%v
           cd windows || exit /b
           "c:\Program Files (x86)\NSIS\makensis" /DVersion2=%ver% /DEmbedD2Dir=..\dmd.windows\dmd2 d2-installer.nsi || exit /b
+          ren dmd-%ver%.exe dmd-${{ inputs.release_branch }}.exe || exit /b
           copy dmd-*.exe ..\create_dmd_release\build || exit /b
 
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