Fix module tests on Visual Studio builds

On Visual Studio, Meson builds modules as xxxx.dll, not libxxxx.dll when
xxxx is specified as the name for the shared_module() build directive.

This means that in the test programs if we expect for libxxxx for the
module name, the test will fail as there is no libxxxx.dll but there is
xxxx.dll.  This makes the test program look for the module files
correctly.
11 jobs for fix-module-tests-msvc in 18 minutes and 8 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #335303
cross-android_api21_arm64

00:01:49

passed #335304
cross-android_api28_arm64

00:01:50

passed #335305
cross-mingw64

00:03:18

passed #335301
debian-stable-x86_64

00:02:19

passed #335300
fedora-x86_64

00:06:00

passed #335308
freebsd-11
freebsd-11-x86_64

00:03:58

passed #335302
G_DISABLE_ASSERT

00:03:59

passed #335306
win32
msys2-mingw32

00:08:47

passed #335307
win32
vs2017-x64

00:09:12

 
  Coverage
passed #335309
coverage

00:01:17

77.9%
 
  Analysis
passed #335310
scan-build

00:04:20