RFR: 8375692: Hotspot container tests assert with non-ascii vendor name [v3]

[Severin Gehwolf]

> Please review this test-only fix. For non-ascii vendor strings the hotspot container tests fail in fastdebug because the encoding of the vendor string doesn't match. Full details in [JDK-8375471](https://bugs.openjdk.org/browse/JDK-8375471). In order to avoid the assert, the containers need to set to an UTF-8 encoding. This patch proposes to do so by setting `LANG=C.UTF-8`.
> 
> Thoughts?
> 
> **Testing:**
> - [x] GHA
> - [x] Linux container tests on cg v1 and cg v2 with a JDK build and vendor string `Foo bar öÜß` and fastdebug. All pass. Most failed before.

Severin Gehwolf has updated the pull request incrementally with one additional commit since the last revision:

  Restore Bellsoft copyright

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/29315/files
  - new: https://git.openjdk.org/jdk/pull/29315/files/9f93451f..e539a64f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29315&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29315&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29315.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29315/head:pull/29315

PR: https://git.openjdk.org/jdk/pull/29315