Adjust trixie to avoid too much riscv64

[tianon]

Trixie doesn't yet have git (probably more), but curl does build successfully, so this adjusts generate-stackbrew-library.sh to exclude riscv64 from all but trixie-curl.

$ diff -u <(bashbrew cat buildpack-deps) <(bashbrew cat <(./generate-stackbrew-library.sh))
--- /dev/fd/63  2024-08-13 10:59:42.728567215 -0700
+++ /dev/fd/62  2024-08-13 10:59:42.732567254 -0700
@@ -47,7 +47,7 @@
 Directory: debian/sid

 Tags: trixie-curl, testing-curl
-Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, s390x
+Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, riscv64, s390x
 GitCommit: 1f4fe499c668d9a2e1578aa8db4f0b2d14482cf5
 Directory: debian/trixie/curl

[tianon]

Oh, because it's probably helpful context, here's that same command run on current master instead (ie, without this PR):

$ diff -u <(bashbrew cat buildpack-deps) <(bashbrew cat <(./generate-stackbrew-library.sh))
--- /dev/fd/63  2024-08-13 11:05:02.111584348 -0700
+++ /dev/fd/62  2024-08-13 11:05:02.111584348 -0700
@@ -47,17 +47,17 @@
 Directory: debian/sid

 Tags: trixie-curl, testing-curl
-Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, s390x
+Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, riscv64, s390x
 GitCommit: 1f4fe499c668d9a2e1578aa8db4f0b2d14482cf5
 Directory: debian/trixie/curl

 Tags: trixie-scm, testing-scm
-Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, s390x
+Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, riscv64, s390x
 GitCommit: 1f4fe499c668d9a2e1578aa8db4f0b2d14482cf5
 Directory: debian/trixie/scm

 Tags: trixie, testing
-Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, s390x
+Architectures: amd64, arm32v5, arm32v7, arm64v8, i386, mips64le, ppc64le, riscv64, s390x
 GitCommit: 1f4fe499c668d9a2e1578aa8db4f0b2d14482cf5
 Directory: debian/trixie