HADOOP-19777: Update trunk BUILDING.txt for Java 17 requirement

[cnauroth]

Description of PR

Update Java 8 references in BUILDING.txt to say Java 17 instead.

How was this patch tested?

Documentation change only.

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	9m 26s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+0 🆗	detsecrets	0m 0s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
			_ trunk Compile Tests _
+1 💚	shadedclient	18m 8s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	shadedclient	13m 27s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	asflicense	0m 20s		The patch does not generate ASF License warnings.
		43m 4s

Subsystem	Report/Notes
Docker	ClientAPI=1.52 ServerAPI=1.52 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8167/1/artifact/out/Dockerfile
GITHUB PR	#8167
Optional Tests	dupname asflicense codespell detsecrets
uname	Linux 39064df664c3 5.15.0-164-generic #174-Ubuntu SMP Fri Nov 14 20:25:16 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / 4347364
Max. process+thread count	636 (vs. ulimit of 5500)
modules	C: . U: .
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8167/1/console
versions	git=2.25.1 maven=3.9.11
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[ayushtkn]

LGTM

[pan3793]

recent version of macOS removes the built-in script languages, so it should use a different command that does not rely on OS Ruby to install homebrew

- * Install OpenJDK 8
+ * Install OpenJDK 17

brew main repo has openjdk@17 so no need for brew tap AdoptOpenJDK/openjdk