Leverage "shivammathur/setup-php" action for "ibm_db2" extension install

[phansys]

Q	A
Type	improvement
Fixed issues	n/a

Summary

Use the provided options instead of the manual install.
It also prevents this warning, that occurs in the current setup because the order of the install commands:

PHP Warning:  PHP Startup: Unable to load dynamic library 'ibm_db2.so' (tried: /usr/lib/php/20220829/ibm_db2.so (/usr/lib/php/20220829/ibm_db2.so: cannot open shared object file: No such file or directory), /usr/lib/php/20220829/ibm_db2.so.so (/usr/lib/php/20220829/ibm_db2.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0

[greg0ire]

Thanks @phansys !