lib data model serialization: don't claim support on PHP < 7.4

The syntax of the library (at least test code) is no
longer compatible with PHP < 7.4.
Cannot automatically test the library code on
obsolete PHP versions, so do not claim support for these.
PHP 7.4 kept as it is the version used in the WMF
environment as of this writing.

Bug: T381168
Change-Id: Ifcec5ece2204cae2c563b551e09616116c1d6f78

Author: manicki

.github/workflows/lint-and-test.yaml

@@ -8,7 +8,7 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                php_version: [ '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4' ]
+                php_version: [ '7.4', '8.0', '8.1', '8.2', '8.3', '8.4' ]
         steps:
             - uses: actions/checkout@v4
             - name: Setup PHP

composer.json

@@ -31,7 +31,7 @@
 		"irc": "irc://irc.libera.chat/wikidata"
 	},
 	"require": {
-		"php": "^7.0|^8.0",
+		"php": "^7.4|^8.0",
 		"wikibase/data-model": "~9.0|~8.0",
 		"serialization/serialization": "~4.0|~3.1",
 		"data-values/serialization": "~1.0"