Prepare for 2026-03 RC1

- Use https://download.eclipse.org/releases/2026-03/202602271000/
- Update +1s for M3 responses

Part of #422

Author: merks

releng/org.eclipse.epp.config/parent/pom.xml

@@ -41,7 +41,7 @@
     <!-- Name release directory on download.eclipse.org -->
     <RELEASE_DIR>202602261000</RELEASE_DIR>
     <!-- SimRel Repo to build from -->
-    <SIMREL_REPO>https://download.eclipse.org/staging/2026-03/</SIMREL_REPO>
+    <SIMREL_REPO>https://download.eclipse.org/releases/2026-03/202602271000/</SIMREL_REPO>
     <!-- ID used to generate the filename of the packages -->
     <eclipse.simultaneous.release.id>${RELEASE_NAME}-${RELEASE_MILESTONE}</eclipse.simultaneous.release.id>
     <!-- Timestamp used in various places, e.g. the about dialog (see about.mappings) -->

releng/org.eclipse.epp.config/tools/upload-to-staging.sh

@@ -59,14 +59,14 @@ Last +1 received for each package and platform (apologies if I missed one of you
 Packages:
 committers - 2025-12 M1 
 cpp - 2026-03 M2
-dsl - 2025-12 RC2
+dsl - 2026-03 M3 
 embedcpp - 2026-03 M2
 java - 2025-06 RC1
-jee -  2025-12 RC1
+jee -  2026-03 M3
 modeling - 2026-03 M2
 php - 2025-12 RC1 
 rcp - 2025-06 RC2
-scout - 2026-03 M2
+scout - 2026-03 M3
 
 Platforms:
 Linux x86_64 - 2026-03 M2
@@ -75,7 +75,7 @@ Linux riscv64 - 2025-12 M1
 Windows x86_64 - 2026-03 M2
 Windows on Arm - 2025-12 RC1
 macOS x86_64 - 2026-03 M1
-macOS aarch64 - 2026-03- M2
+macOS aarch64 - 2026-03- M3
 
 Thank you for testing!