chore: revert a workaround with Python 3.6 installation

 Relate to #1533 and #1154

[skip ci]

Author: php-coder

docs/decisions-log.md

@@ -2,7 +2,7 @@
 
 | Date/Type | Description |
 | --------- | ----------- |
-| 09.07.2022 Workaround | [php-coder/mystamps#1533](https://github.com/php-coder/mystamps/issues/1533): After update of **html5validator** to 0.4.2, it has turned out that, starting from 0.4.0, it requires **Python** 3.6 that we don't have on Travis CI as we still on the old Ubuntu 16.04. Until we migrate to 20.04. (see [php-coder/mystamps#1467](https://github.com/php-coder/mystamps/issues/1467)), I decided to install Python 3.6 manually. Commits: [0e09fac8](https://github.com/php-coder/mystamps/commit/0e09fac8663d6642e13c7c413d550da163d4fa95)
+| ~~09.07.2022 Workaround~~ | ~~[php-coder/mystamps#1533](https://github.com/php-coder/mystamps/issues/1533): After update of **html5validator** to 0.4.2, it has turned out that, starting from 0.4.0, it requires **Python** 3.6 that we don't have on Travis CI as we still on the old Ubuntu 16.04. Until we migrate to 20.04. (see [php-coder/mystamps#1467](https://github.com/php-coder/mystamps/issues/1467)), I decided to install Python 3.6 manually. Commits: [0e09fac8](https://github.com/php-coder/mystamps/commit/0e09fac8663d6642e13c7c413d550da163d4fa95)~~<br />UPDATE(03.12.2022): in [d2110ff6](https://github.com/php-coder/mystamps/commit/d2110ff651e84a32e25cc83cd4208d357f59791c) commit I reverted this workaround because it's no longer required: as part of migration to GitHub Actions ([php-coder/mystamps#1154](https://github.com/php-coder/mystamps/issues/1154)), since commit [661444c6](https://github.com/php-coder/mystamps/commit/661444c62d91694b628351b34724fdc6d999f5a4) we use a container with Ubuntu 20.04 and Python 3.8.10 |
 | 22.01.2022 Workaround | [php-coder/mystamps#1549](https://github.com/php-coder/mystamps/issues/1549): During update of **Liquibase** from 4.5.0 to 4.7.1 a new issue has been popped up: starting from 4.7.1 it logs all applied migrations to the console. And it seems like it logs directly and it doesn't respect logger configuration. It has a low impact to production but in test environment it spams a lot as we always apply all existing migrations. Moreover, it also affects unit tests where we use in-memory database. I raised this question in upstream (see my comments in [liquibase/liquibase#2200](https://github.com/liquibase/liquibase/pull/1932#discussion_r790117453)) but it might be an issue on our side as we use the latest Liquibase and (very old) Spring Boot 2.1.18 Commits: [f3c2e20d](https://github.com/php-coder/mystamps/commit/f3c2e20d1ba78703f53b6b090bfe7f7257e34a04)<br />UPDATE(24.01.2022): Bug: [liquibase/liquibase#2396](https://github.com/liquibase/liquibase/issues/2396) |
 | 10.11.2021 Workaround | [php-coder/mystamps#1549](https://github.com/php-coder/mystamps/issues/1549): During update of **Liquibase** from 4.5.0 to 4.6.1 the bug has been faced -- the migration `0.4/2017-05-29--test_image.xml` has started to fail with error `BLOB resource not found: /test/test.png`. I postponed this update and filled a bug report to upstream. Bug: [liquibase/liquibase#2200](https://github.com/liquibase/liquibase/issues/2200)<br />UPDATE(22.01.2022): in [f3c2e20d](https://github.com/php-coder/mystamps/commit/f3c2e20d1ba78703f53b6b090bfe7f7257e34a04) I have updated Liquibase to the latest version and also I applied a workaround by specifying a relative path instead of an absolute one. The future of the bug report isn't clear at this moment: it's definitely broke the backward compatibility and even a workaround requires us to modify the existing migration (that we mustn't do! but we can as this particular migration is used only by tests). From another hand, this change was made intentionally and it might stay with us forever |
 | 02.07.2021 Workaround | Enablement of `GuardLogStatement` in **PMD** led to a few false positives when we concatenate constant string literals. This should be fixed in PMD >= 6.36.0 but until we have this version (see [php-coder/mystamps#1250](https://github.com/php-coder/mystamps/issues/1250)), I suppressed violations manually. Bug: [pmd/pmd#957](https://github.com/pmd/pmd/issues/957) Commits: [0b135cb4](https://github.com/php-coder/mystamps/commit/0b135cb41f2da6d5ffc6570acf0ae68db35295f7) |