feat(cloud_sql/mysql): update to V2 sample

[jsimonweb]

• Update region tags
• Update DB_HOST env. variable to be INSTANCE_HOST
• Add INSTANCE_UNIX_SOCKET env. variable

[snippet-bot]

Here is the summary of possible violations 😱

Details

There is a possible violation for removing region tag in use.

• cloud_sql/mysql/pdo/src/app.php:39, tag cloud_sql_mysql_pdo_timeout(usage: page 1).

The end of the violation section. All the stuff below is FYI purposes only.

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You are about to delete the following sample browser pages.

• cloud_sql/mysql/pdo/src/DBInitializer.php:45, tag cloud_sql_mysql_pdo_create_tcp(usage: page 1).
• cloud_sql/mysql/pdo/src/DBInitializer.php:104, tag cloud_sql_mysql_pdo_create_socket(usage: page 1).
• cloud_sql/mysql/pdo/src/app.php:39, tag cloud_sql_mysql_pdo_timeout(usage: page 1).

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You are about to delete the following frozen region tags.

• cloud_sql/mysql/pdo/src/DBInitializer.php:45, tag cloud_sql_mysql_pdo_create_tcp(usage: page 1 page 2 page 3 page 4 page 5 page 6 page 7 page 8).
• cloud_sql/mysql/pdo/src/DBInitializer.php:104, tag cloud_sql_mysql_pdo_create_socket(usage: page 1 page 2 page 3 page 4 page 5 page 6 page 7 page 8).

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Here is the summary of changes.

You are about to add 3 region tags.

• cloud_sql/mysql/pdo/src/DatabaseTcp.php:20, tag cloud_sql_mysql_pdo_connect_tcp
• cloud_sql/mysql/pdo/src/DatabaseTcp.php:51, tag cloud_sql_mysql_pdo_timeout
• cloud_sql/mysql/pdo/src/DatabaseUnix.php:20, tag cloud_sql_mysql_pdo_connect_unix

You are about to delete 3 region tags.

• cloud_sql/mysql/pdo/src/DBInitializer.php:45, tag cloud_sql_mysql_pdo_create_tcp
• cloud_sql/mysql/pdo/src/DBInitializer.php:104, tag cloud_sql_mysql_pdo_create_socket
• cloud_sql/mysql/pdo/src/app.php:39, tag cloud_sql_mysql_pdo_timeout

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[bshaffer]

These values will never equal true... they're either false or a string

https://www.php.net/manual/en/function.getenv.php

[bshaffer]

The !== means exactly true, so this condition will always be pass. It should be:

if (getenv('DB_USER') === false) {

[jsimonweb]

Updated.