meson: Fix SONAME for unstable versions

Replacing the string is not enough [^] for e.g. nixpkgs precise versions:

`2.31pre20250712_b1245123`

[^]: NixOS/nixpkgs#444089

Author: xokdvium

nix-meson-build-support/common/meson.build

@@ -42,4 +42,4 @@ if cxx.get_id() == 'clang' and ('address' in get_option('b_sanitize') or 'undefi
 endif
 
 # Darwin ld doesn't like "X.Y.Zpre"
-nix_soversion = meson.project_version().replace('pre', '')
+nix_soversion = meson.project_version().split('pre')[0]