[rhythmbox] Use a specific version of meson for CI builds

[Jonathan Matthew <jmatthew src gnome org>]

commit 9281f532631095ff521c3577026cd0ad05120e57
Author: Jonathan Matthew <jonathan d14n org>
Date:   Mon Jan 17 16:10:58 2022 +1000

    Use a specific version of meson for CI builds
    
    I'll deal with the pointless syntax changes at my own pace thank you

 .gitlab-ci.yml | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8dac783ad..ba30c616f 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -4,6 +4,8 @@ stages:
   - test
 
 variables:
+  MESON_VER: 0.60.3
+
   UBUNTU_DEPS:
     build-essential
     gtk-doc-tools
@@ -60,7 +62,7 @@ before_script:
   - export DEBIAN_FRONTEND=noninteractive
   - apt-get update
   - apt-get install -y $UBUNTU_DEPS
-  - pip3 install meson
+  - pip3 install meson==$MESON_VER
 
 test:
   stage: test