Fix Meson error when test dependencies are missing.

Based on this upstream commit, with some adjustments to apply on 2.8.0:
https://gitlab.freedesktop.org/spice/libcacard/-/commit/cf6121deb47e437aa566cfeb29a03da93c432394

diff --git a/tests/meson.build b/tests/meson.build
index 87945a2..baefaf5 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -9,15 +9,6 @@ modutil_dep = find_program('modutil', required: false)
 openssl_dep = find_program('openssl', required: false)
 softhsm_util_dep = find_program('softhsm2-util', required: false)
 
-if pkcs11_tool_dep.found() and p11tool_dep.found() and modutil_dep.found() and openssl_dep.found() and softhsm_util_dep.found()
-  softhsm = custom_target(
-    'softhsm2.conf',
-    command: find_program('setup-softhsm2.sh'),
-    capture: true,
-    output: 'setup-softhsm2.log',
-  )
-endif
-
 libcacard_test = executable(
   'libcacard',
   ['libcacard.c', 'common.c'],
@@ -64,9 +55,18 @@ hwtests_test = executable(
   dependencies: [libcacard_dep],
 )
 
-test(
-  'hwtests',
-  hwtests_test,
-  depends: [softhsm],
-  env: env,
-)
+if pkcs11_tool_dep.found() and p11tool_dep.found() and modutil_dep.found() and openssl_dep.found() and softhsm_util_dep.found()
+  softhsm = custom_target(
+    'softhsm2.conf',
+    command: find_program('setup-softhsm2.sh'),
+    capture: true,
+    output: 'setup-softhsm2.log',
+  )
+
+  test(
+    'hwtests',
+    hwtests_test,
+    depends: [softhsm],
+    env: env,
+  )
+endif
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<div class='path'>path: <a href='/guix/log/?id=9dea3f101f252331c049c03f501398a5ec837ba9'>root</a>/<a href='/guix/log/gnu?id=9dea3f101f252331c049c03f501398a5ec837ba9'>gnu</a>/<a href='/guix/log/gnu/packages?id=9dea3f101f252331c049c03f501398a5ec837ba9'>packages</a>/<a href='/guix/log/gnu/packages/patches?id=9dea3f101f252331c049c03f501398a5ec837ba9'>patches</a>/<a href='/guix/log/gnu/packages/patches/guile-fibers-destroy-peer-schedulers.patch?id=9dea3f101f252331c049c03f501398a5ec837ba9'>guile-fibers-destroy-peer-schedulers.patch</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/patches/guile-fibers-destroy-peer-schedulers.patch?id=9dea3f101f252331c049c03f501398a5ec837ba9&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-05-22 14:32:07 -0500'>2020-05-22</span></td><td><a href='/guix/commit/gnu/packages/patches/guile-fibers-destroy-peer-schedulers.patch?id=9af90aafdfd8afd5fb7b5377ca5daf2215d38d7a'>gnu: guile-fibers: Add patch to fix resource leak.</a><span class='msg-avail'>...<span class='msg-tooltip'>guile-fibers@1.0.0 has a resource leak where run-fibers will only destroy one
scheduler, but it creates as many as there are cpu cores by default (see
https://github.com/wingo/fibers/issues/36).  This causes the tests to fail on
systems with many cores, and can cause guile to crash under certain
circumstances.  This fixes that resource leak.  At present neither git master
nor the latest release has fixed this yet.

* gnu/packages/patches/guile-fibers-destroy-peer-schedulers.patch: New patch.
* gnu/local.mk: Add it to the list of patches.
* gnu/packages/guile-xyz.scm (guile-fibers): Use it.
</span></span></td><td>Caleb Ristvedt</td></tr>