build: Bump js-shell used for syntax checks

gjs moved from SpiderMonkey 52 to 60 during the last cycle, it's time
we follow suit.

.gitlab-ci.yml

@@ -4,7 +4,7 @@ stages:
  - build
 
 before_script:
-  - dnf install -y meson gettext mozjs52-devel
+  - dnf install -y meson gettext mozjs60-devel
 
 build-shell-extensions:
   stage: build

extensions/meson.build

@@ -33,11 +33,11 @@ install_data (extension_schemas,
 )
 
 foreach js_source : js_sources
-  if (js52.found())
+  if (js60.found())
     path_array = '@0@'.format(js_source).split('/')
     name = join_paths(path_array[-2], path_array[-1])
 
-    test('Checking syntax of ' + name, js52,
+    test('Checking syntax of ' + name, js60,
       args: ['-s', '-c', js_source],
       workdir: meson.current_source_dir()
     )

meson.build

@@ -22,7 +22,7 @@ xsessiondir = join_paths(datadir, 'xsessions')
 
 extensionlib = files('lib/convenience.js')
 
-js52 = find_program('js52', required: false)
+js60 = find_program('js60', required: false)
 
 ver_arr = meson.project_version().split('.')
 if ver_arr[1].to_int().is_even()