Merge #115503

115503: clusterversion: README.md: remove previous version step r=RaduBerinde a=RaduBerinde

The runbooks were written under the assumption that we will gate the
support of version skipping during upgrade using an env var.

We have decided this is not really necessary, given that we'll have
tests for this throughout the 24.1 cycle. The `PreviousRelease`
constant (which used to be the version we *do* support without the env
var) doesn't play an important role anymore.

This commit removes the step related to bumping `PreviousRelease`. We
will keep it as is currently defined in the code: a simple alias for
the last entry in `SupportedPreviousReleases()`.

Epic: none
Release note: None

Co-authored-by: Radu Berinde <[email protected]>

pkg/clusterversion/README.md

@@ -21,15 +21,13 @@ graph TD;
   base("Cut release-24.1 branch
         Latest = 23.2-x
         MinSupported = 23.1
-        PreviousRelease = 23.2
         version.txt = v24.1.0-alpha.00000000")
     
   base -- release-24.1 --> rel1
   
   rel1("R.1: Prepare for beta
         Latest = 23.2-x
         MinSupported = 23.1
-        PreviousRelease = 23.2
         developmentBranch = false
         version.txt = v24.1.0-beta.1")
   
@@ -38,7 +36,6 @@ graph TD;
   rel2("R.2: Mint release
         Latest = 24.1
         MinSupported = 23.1
-        PreviousRelease = 23.2
         developmentBranch = false
         finalVersion = V24_1
         version.txt = v24.1.0")
@@ -49,28 +46,18 @@ graph TD;
   master1("M.1: Bump min supported
            Latest = 23.2-x
            MinSupported = 23.2
-           PreviousRelease = 23.2
            version.txt = v24.1.0-alpha.00000000")
             
   master1 --> master2
     
   master2("M.2: Bump current version
            Latest = 24.1-2
            MinSupported = 23.2
-           PreviousRelease = 23.2
            version.txt = v24.2.0-alpha.00000000")
             
   master2 --> master3
             
-  master3("M.3: Bump previous release
-           Latest = 24.1-x
-           MinSupported = 23.2
-           PreviousRelease = 24.1
-           version.txt = v24.2.0-alpha.00000000")
-            
-  master3 --> master4
-
-  master4(M.4: Finalize gates and bootstrap data for released version)
+  master3(M.3: Finalize gates and bootstrap data for released version)
 ```
 
 ## Release branch changes
@@ -213,31 +200,12 @@ necessary if the current runbooks are followed).
 
 **Example PR:** [#112271](https://github.com/cockroachdb/cockroach/pull/112271)
 
-### M.3: Bump previous release
-
-**What**: `PreviousRelease` is the version from which we the Cockroach binary
-supports upgrades (without enabling experimental version skipping). This value
-can only be updated once a beta version for that release is published (and
-listed as a "predecessor version" in
-`pkg/testutils/release/cockroach_releases.yaml`); this is because upgrade tests
-attempt to download the published version to test against.
-
-**When**: Any time after publishing the first beta from the forked release (and
-after M.2).
-
-**Checklist**:
-- [ ] Advance `PreviousRelease` to match the in-progress release
-- [ ] Regenerate expected test data results as needed; file issues for any
-  skipped tests.
-
-**Example PR:** TODO
-
-### M.4: Finalize gates and bootstrap data for released version
+### M.3: Finalize gates and bootstrap data for released version
 
 **What**: Bring in any last changes to bootstrap data and version gates from the
 release.
 
-**When**: Any time after minting the previous release (R.2), and after M.3.
+**When**: Any time after minting the previous release (R.2), and after M.2.
 
 **Checklist**: